Carburettor Cleaning FAQ
by Kristian #562
Please read the Disclaimer before attempting any work in this FAQ.

• Carb Nomenclature
• Why should I clean out/re-condition my Carburettor:
• General FAQ’s about the F650 Carbs
• So how do I get the Carb Out
• Enough of the Preamble, How do I actually Clean & Replace Carb Parts.
• How Do I Replace the Carbs.
• Inline Filter
• Carburettor LINKS
• Checking the Float Height with the Carbs ON the bike?
• Opinions (On Carb Cleaning/Particular Parts Replacement).
• Detailed Feedback on Carb Reconditioning
• Identifying a Float Valve Problem

Looking for the OEM Inline Filter ?  or the Aftermarket Fuel Filter?

Please Note that this FAQ only deals with the resetting of your Carb to the STOCK configuration. Re-Jetting, Needle Changes and Modifying Float Heights are covered to some extent in the Exhaust-Rejetting Spreadsheet. Have a look there if this is the kind of information you need. Nor is this a treatise on how a Carb Works. There are lots of references about that on the Web. I will try and add some links I think are worthwhile references, at a later date, as I come across them. Perhaps you might like to suggest some too. Dynojet has pretty good simple one here: Dynojet’s Carb Theory. I need to refine some parts of the pictures and circle some specific parts of the photos, and I need a few additional pictures. Write to me and tell me what you think would make it better.

• Refer the Carbs Misc. FAQ for other information on Carbs.
• Refer also the General Performance Modifications Guidelines & Tips, Dynojet Settings, Snorkel, Organ Pipes, Alternative Carbs & Carb Parts.
• Refer the JetKit FAQ for information on Length of Carb Springs etc, if you're not sure your bike has part of, or an entire Jet Kit.
• Refer the Idle Mix Screw FAQ for where it is and Tips on Adjustment.

Carb Nomenclature:

Note that Slide is also often called Slide Piston (or Piston) or Slide Barrel. The Slide Carrier is often just referred to as the Carrier.

Why should I clean out/re-condition my Carburettor?  

A.

1. If you've read the Hard Starting FAQ and the Poor Mileage FAQs and nothing helps.

2. When the bike has been standing a long time and it sputters and stalls and pops and wheezes (but try some carb cleaner in a tankful of gas first! ) and you’re worried (or you know) the rubber O-Rings have deteriorated.

3. When the bike falls victim to the Pukin’ Petrol Syndrome and you have to take it out anyway for that reason.

4. When the bike “bogs down” at  anything above just past idle, a sign of a Split Diaphragm and you KNOW it’s not your Voltage Rectifier or Plugs or Plug-Caps.

5. When you are getting Poor Gas Mileage.

6. When you are Rejetting (Warning, Rejetting is a long slow process and you may NEVER be satisfied with the results).

7. When your bike seems to Surge or Stumble (even if it is NOT an F650GS) and you KNOW it’s not your Chain/Sprockets or a dirty Air Filter.

General FAQ’s about the F650 Carbs

• Reduction in mileage?
• Gas mileage?
• Who makes the F650 Carb?
• Another bike with the same carb?
• Another supplier?
• Synchronise?
• STOCK Carb Settings?
• Carb Parts Numbers?
• Websites to tell me how to tune my Carb?
• What Parts of the Carb get worn?
• What about alternative Sources for the O-Rings?
• Adjust the Idle MIX Screws

Q. At what mileage can I expect to get a reduction in mileage due to worn Carb parts?
A. This is an extremely difficult question to answer, it depends on whether you ride in dirt, road or at cruise revs or high revs. Some inmates have noted a decrease in Gas Mileage around the 20,000 miles mark.

Q. So what gas mileage should I expect to get?
A. Again this is an extremely difficult question to answer, it depends on whether you ride in dirt, road or at cruise revs or high revs. Some inmates get 45-50, some 50-55, some 55-60. If you get less than 45-50 with a stock bike, normal around town riding on the road, and you have a high mileage bike, it’s probably time to check the Carbs. Same goes if you get less than about 50-55 on the open road. Refer the Poor Mileage FAQ for more details/feedback.

Q.  Who makes the F650 Carb?
A.  Mikuni. They are 2 x 36mm Mikuni BST B316 CV (Constant Velocity) Carburettors. There are two on the F650, side by side.

Q.  Is there another bike with the same carb. from which I can scavenge cheap Bike Parts.
A.  Yes, the Aprilia Pegaso, a 5-Valve Aprilia version of the bike, made in the same factory in Italy. It’s not identical though. You can also get SOME parts from the Suzuki GS500E Carb, which is very similar. Refer Alternative Carbs & Carb Parts for details.

Q.  Is there another supplier that supplies parts?
A.  If it’s just Main and Pilot Jets you are after you can probably get them from your local Bike Shop. Ask for Mikuni Jets and show them your old ones, as there are several different head Styles. I know you can get them from to Sudco-Mikuni in the U.S. however Sudco do NOT supply the needles. They say they were a special run for BMW and I’ve found the only supplier to be BMW or a BMW Agent. However Dave #365 (Thank you Dave !) got this precious Gem:

Q.  Do I need to “Balance” (Synchronise) the Carbs.
A.  You have probably read somewhere about needing to “balance” the Carbs. This really applies to multi-cylinder engines where individual Carbs feed individual Cylinders. You do NOT need to “Balance” the carbs on the F650 if you set the “Settings” (Needle, Float/Jet Size/Mix Screw)  the same, for each Carb. It’s a single cylinder engine. For more information refer The Carb Misc FAQ.

Q.  What are the STOCK Carb Settings?
A. The Stock Carb Settings are:

• 1996 Onward Models:
• Main Fuel Jets #132.5
• Pilot Jets #41.3 (Idle Air Jets)
• Needles 5E94, 4th Clip from Top (Blunt End)
• Carb Venturi (Emulsion Tube) 584□□-2. The first "□" stands for  a rectangle with a small square inside, the second "□" stands for a small rectangle. Thanks to Marty #436)
• Float Height 14.6mm from the Gasket Surface
• Idle Mix Screws backed out 3.5 turns from LIGHTLY seated (all the way in).
• The Stock "Organ Pipe's are sealed so if yours are open someone has probably re-jetted your bike.

1993-1995 Models:  Thanks to Spakur & Fede

• Main Fuel Jets #140
• Main Air Jet 0.6
• Pilot Jets #41.3 (Idle Fuel Jets)
• Idle Air Jet 1.5
• Needles 5E94, 4th Clip from Top (Blunt End)
• Carb Venturi 584#0-2
• Float Height 14.6mm from the Gasket Surface.
• Idle Mix Screws backed out 3.5 turns from LIGHTLY seated (all the way in).
• The Stock "Organ Pipe's are open so if yours are plugged someone has probably re-jetted your bike. Here's a picture of a 1995 with the holes ALREADY open, from the factory: Factory Airbox.

Q. What are the Carb Parts Numbers?
A. Steve#417 supplied these: (Thanks Steve)

• 13112343398 Valve Assembly
  13112343379 Diaphragm
  13112343397 Needle
  13112343395 Venturi Jet
  13112343318 Idle Jet
  13112343412 O-ring (idle mixture)
  13112343404 Bracket Float (with O-ring)

        Here is the OEM Parts List:

• FCarbParts1

• FCarbPartsList1

• FCarbParts2

• FCarbPartsList2

• FCarbParts3

• FCarbPartsList2

Refer also the Carb Alternatives

Q. Are there any Websites to tell me how to tune my Carb?
A. Well the best thing you can do if you have a Stock Setup or even Stock Carb with an aftermarket exhaust is to Check for and Replace all the worn parts discussed above and set the Carburettor Floats/Idle Screw/Clip Location to the specified Stock Settings. Otherwise:

• Factory’s is pretty good: Factory Pro's CV Tuning FAQ. Their approach is to tune the Carburettor from the Main Jet size and work DOWN through the Needle Clip Setting, Float Bowl Height, (SOMETIMES Pilot jet) and then the Idle Mixture Screw.

• Sudco have a Manual, called the Sudco-Mikuni Manual which I cannot give you because it is copyrighted, however they work UP from the Idle Mixture Screw , Pilot Jet, Needle Clip Settings, Float Bowl Height to the Main Jet size and claim that each of the Carburettor Circuits are additive. See Sudco Carbs 1 & Sudco Carbs 2.

• Dynojet gives you the Needle and the Main Jets and says THESE are the settings, if it doesn’t work , try the needle one clip either way, then adjust the Float Bowl Height. Do NOT change the Pilot Jet.

• These last three you SHOULD only need if you rejet, which can be a REAL Trial. (PITA)

• There is also a good list at the Bottom of the Page.

Q. What Parts of the Carb get worn?
A. Pretty much all the moving parts or parts against which moving parts work, like any mechanical device. However there are some parts which don’t move that deteriorate with age, some to a greater extent than others. The parts that most often wear or deteriorate are the Carb-O-Rings, Needles (shown are the Stock (L) vs. Dynojet (R) needles), Diaphragm Rubbers (shown on top of the Slide), Slide Carrier (Grey Plastic Block) and the Slide (Black barrel with two Side Fins). The jets (Main Jet, Pilot Jet) do not really wear, except for the so-called Carb Venturis or “Needle Jets”, due to the action of the needle vibrating within in it. Here's a link to an Oblong Venturi Jet, on Factory Pro's Website, to give you some idea of the wear that can occur in the needle jet. It is this wear, along with the corresponding rubbing/scratching of the needle. See Worn Needles, also on Factory’s Site. However if the gas is dirty the Main or Pilot Jets can also get blocked (fairly common) and the hole CAN wear bigger, although this is not that common. The Float Valve Tips and or Springs can also wear, but take a bit longer than other parts.

AND.... Don't forget to check the rubber intake manifold for cracks as well as the rubber Air-intake boot.!

One thing you might also want to watch out for. If you've been using Coolant with Silicates in it, (which you should NOT as it will destroy your water pump), you might accidentally spill some into the intake snorkel when you fill your coolant and the fine Silicates that may pass through the Air Filter will quickly wear your Carb Venturis and Needles.

The sizes of the Four Replaceable O-Rings, (4 in EACH Carb i.e. Total 8) available from any bearing shop are, Smallest to Largest:

• Idle-Mix Screw O-ring: 1 x 2.5 (or 1 x 3). I found that the 1 x 3mm O-ring was the closest fit for the idle mix screw (vs. the 2.5 in the FAQ). Actually, the 1 x 2.5 is closer on the ID, and the 1 x 3 is exact for the OD. Marty #436) . Idle-Mix Screw O-ring: 1 x 2.5 (BMW Part # 13 11 234 3 412)

• Float Frame O-ring:  1.5 x 5

• Float Valve Seat O-ring: 1.5 x 7

• Slide O-ring: 1.5 x 10

• Where the first number is the O-Ring thickness and the second is the internal diameter, both in mm.

• Buy at least two of each, but get even more, say 4 of each, as they are really cheap and you might even break or lose one putting them back.

• Seriously Consider buying Allen Screws (or Socket Head Cap Screws - SHCS) for the Float Bowls (and also possibly for the Diaphragm Cover Cap Screws, though not as likely to be stripped).

• You MIGHT strip one of those float bowl screws trying to get it out. e.g. Simon in Ireland notes: I found the float bowl screws difficult to budge - solution = get an impact driver!

Q. What about alternative Sources for the O-Rings?
A.

• Either but generic as noted above or try a Suzuki Dealer for the "O" rings. Viton 5.7X1.3 Part # 8-4602 fits the tiny 1X2.5mm one for the float bowl assembly.

• The 1.5X5mm one is #13374-35C00 from Suzuki. That seals the float seat. These two should cure your "drips".

• Now beware. These stupid "o" rings can cost $2-4 each. That's silly but much better than the parts with "O" rings from BMW. I think the seat, needle and "O" ring alone for one side is about $32 plus tax and jar of Vaseline. Then you have to buy a complete new float assembly and that's more ridiculous.

• Don't break your float bowl gaskets. They are $37 each from BMW. Don't know what they are if you run then down from some Jap dealer. (Mal)

Q. How do I adjust the Idle/Adjust the Idle MIX Screws ON the bike. (Note they ARE different).
A. Refer the Idle Mix Screw FAQ.

So how do I get the Carb Out ?

A1.     Complete Carb Removal

1. DON’T SMOKE.

2. Remove the Seat.

3. Remove the Tank See the Gas Tank Removal-Replacement FAQ.

4. Remove the Seating Plate at the Rear of the Tank, held in Place by two 10mm Bolts.

5. Undo the 2 Hose-Pipe Clips on the Air Intake Side (Rear of Carb) and the 2 on the Cylinder Head Side (Front of Carb) and Remove the Carbs.

6. For Carb Removal, see Flash’s FAQ. This is a bit hard on the rubbers and you might think you’re doing some serious damage, but if you do it right and don’t use a sharp screwdriver, it’s fine. The alternative is to remove the exhaust pipe and take out the Airbox, which is VERY time consuming and a Royal PITA. When you do it, in addition to Flash’s great comments I’d recommend pushing each of the Clamps back away from the Carb as you can and also to wear thick cotton gloves for your hands as the Metal edges, specially the Airbox Side are a bit Sharp. Lift the Air-Intake Side up first and get them past the thinner and more pliable Air-intake rubbers, by pushing the rubbers down past the Carb, while simultaneously pulling the Carbs up and out.

7. Unlatch the Throttle Cable. To do this first twist the throttle (at the Carb) against the spring, then with the cable now slack pull the little steel bend out of the socket in the side of the Carb. With the wire now slack, but still attached to the throttle at the Carb, just rotate the cable in its holder at the throttle-mounting until the cylindrical head and the wire come free.

8. Unscrew the Plastic 12mm Nut to the Choke Cable and pull it out gently. You can only use an open ended spanner. Do NOT turn it the wrong way and screw it up tight now (or later) it’s just a PLASTIC Nut and will Break.! Give the Choke Cable Barrel a bit of clean with some “Jif” or some other polishing fluid. If you want to lubricate the choke cable, this is a good time to do it. Recommendations for lubricating cables run from (a). It’s not required because it’s ion a plastic Sheath (I subscribe to this notion, especially for Choke Cable) to (b) Tape a SMALL STRONG plastic bag of cable lubricant around the cable then hang it up higher than your handlebars, leaving it overnight.

9. The Carb is now free for you to work with in a nice warm comfortable and CLEAN environment, all of which are highly recommended.

10. Bear in mind the Carb Bowls are still full of GAS, so undo the Float Bowl Screws (Circled Red) a few turns and rotate the Carbs around until all the GAS you can get out of it comes out. DON’T SMOKE.

A2.     Removal of the Diaphragm Cap only (on the Bike): 

1. DON’T SMOKE.

2. Remove the Seat.

3. Remove the Tank See the Gas Tank Removal-Replacement FAQ.

4. Remove the Seating Plate at the Rear of the Tank, held in Place by two 10mm Bolts.

5. You now have access to the Diaphragm Caps, which after removal allow you to check and replace: The Diaphragm, Slides (But NOT the Slide Carriers), The Needles, Springs, Needle E-Clips, Needle Spacer and Washer. This also allows you to change the E-Clip position or add a small thin washer, for an equivalent ½ E-clip position change, all without removing the carb from the Bike. Great for fine-tuning Rejetting. Not so good if it’s snowing outside and your bike lives outside.

Q. Should I run the carbs dry by turning off the petcock and running the engine until it dies, before I remove the tank? Or, when you remove the tank and drain the fuel hose going from the petcock to the carbs, do the carbs drain too? If not, is there a reason this is not mentioned in the FAQs? (Perhaps work on the carburettors is easier/better with their "bellies full")?
A. No. You don't need to run the carbs dry. After you turn off the Petcock, if you are REALLY paranoid, you CAN empty the bowls using the drain screws if you really want to. (The Drain Screws are here Float Bowl Drain Screws (Circled Red). Wind them out a few turns, either on the bike beforehand (or after you get the Carb's out and rotate the Carbs around until all the GAS you can get out of it comes out). DON’T SMOKE.

Enough of the Preamble, How do I actually Clean & Replace Carb Parts.

• Tools:

1. You should get hold of a can of Carb Cleaner (any Motorbike Shop should have one, or simply use Petrol) and a few small brushes, with soft (non-metallic) bristles that are not affected by Solvents e.g. Carb Cleaner, Petrol.). Do NOT use wire brushes or bristles from wire brushes to clean the jets, you will damage them.

2. You need a Large Thick and Fairly wide Flat-Blade Screwdriver (for removing the Main Jets).

3. You need a Small thin Flat-Blade screwdriver (for removing the Pilot Jets).

4. You need a Medium-Sized fairly Blunt Phillips Screwdriver (for removing the Float Bowl and Diaphragm Cover Screws).

5. The Tools should be fairly new, should NOT be worn and must FIT properly or you will damage the Screws or the Jets, especially the soft Metal of the Jets.

6. If you want to measure the Float Bowl Height which is very tricky but important nevertheless, a pair of callipers is recommended as a minimum. Factory Pro make a Float Bowl Height Measuring Tool, which in my opinion is not very well made and not worth the money, but is useful. If you can make one yourself, go for it.

7. Rags, Fire Extinguisher in case you have an accident.

8. Patience. But don’t open it up and then leave it lying around for weeks, the O-Rings and Gaskets can become dry and brittle and you might lose some of your parts or forget where they go. But you may use the pictures here as a mnemonic if you wish. J.

Q. How do I undo those Float Bowl Screws!
A. This is a good place to discuss the 2 Screws holding on each Float Bowl.

• The Phillips head screws holding the bowls were INCREDIBLY difficult to remove on my 97. I ended up borrowing a friends cordless impact driver to remove them. Use anti-seize on the threads when reassembling or at least a little grease. Chris in Santa Cruz, CA #782

• Better yet, replace them with Allen's (aka Socket Head Cap Screws = SHCS). Flash #412 (CO).

On with the Cleaning.

• Outside of Carb Body. First off give the outside of the Carb a good clean with your brush and Petrol, including the springs and all the nooks and crannies. Clean it and rub it dry with a Rag. Not only will it look good when you put it back, it will stop getting dirt everywhere inside the Carb and it will stop it being a slippery sucker when you work on it.

• Orientation. For purposes of orientation, in this picture, Intake Side, the Black Dome at the TOP Left is the Diaphragm Cap, held in place by two Philips Screws. One of the Float Bowls, the Jets, the Float Frame, the Slides, Slide Carrier and the Diaphragm Caps have already been removed in this picture (RHS). You can see the back of the Slide through the left Carb, and you can see through the right Carb because the Slide has been removed. I recommend you work on ONE Carb at a time, clean it thoroughly, adjust and replace what you need to and then button it back up again. This way you won’t damage any parts in the adjoining Carb, nor will you lose any.

• Access TOP: When you take the Diaphragm Cap off you have access to the Slide Springs,  the Diaphragm, the Needles (Complete with E-Clips and Spacers) the Slides and also (but ONLY when you have unscrewed the MAIN JET INSIDE THE FLOAT BOWL), the Slide Carrier, Slide O-Ring and the Carb Venturi. All these parts come out the TOP of the Carb. The sealing gasket for the Diaphragm Cap is also the Diaphragm itself.

• Access BOTTOM: The Silver Bowl at the bottom left of the Intake Side picture is the Float Bowl also held in place by two Philips Screws. Once removed you have access to the Float Frame, Floats, Float Frame O-ring, Float Valve, Float Valve Seat, Float Valve Seat O-Ring, Float Bowl Gasket,. Main Jet and the Pilot Jet. As mentioned above, you will NOT be able to disassemble the Slide Carrier (out the Top) nor gain access to the Venturi, without first removing the Main Jet.

• Inline Filter. When you pull the Carbs out the Fuel Line to the Petcock come with it. So it doesn’t get in the way while you are Cleaning the rest of your Carbs, undo the spring clip to where the Fuel Line meets the Carbs, in between the Two Carbs. When you pull off the Fuel Line (Do it gently the T-Piece is only Plastic) there is a brown T-Piece which holds the In-line Fuel Filter. Gently pull out this filter by hand and clean it with a little petrol, blowing on the outside to dislodge any particles on the INSIDE. Then put it back in again so it doesn’t get lost or squashed. When you reinsert it try and line it up so that each of the two flat sides faces the direction of each Carb Bowl. This way when goes go in it goes directly into the filter and out through the netting fabric to each carb.

• Butterfly Valves. When you first get the carb out you will see this, on one side: This is the Engine Side of the Carb. The two Brass circular Discs are the Butterfly Valves, which rotate about a Central Pivot and open when you open your throttle. The more you open your throttle, the more and (faster) air passes through and creates a vacuum, sucking up the Petrol from the Float Bowl, through the Carb Venturis. These parts hardly ever need removal or replacement and should be left alone, unless they are obviously “sticking”. i.e. when you manually turn the throttle against the return spring, you can feel they “Jam” for a moment before they open. If there is any dirt stuck in the pivot, give it a bit of a squirt with carb cleaner and clean it with a brush.

• Inspecting the Carb Needles. Take the Carbs and stand them up in your work bench, Float Bowls down. Try to let the Idle Adjustment screw hang over one edge of the bench so you don’t bend it. On one of the Carb Diaphragm Caps, undo the two Philips head screws and remove the Diaphragm Cap. They can be pretty tight, so use some good downward pressure so you don’t mangle the screws. You may even need to gently tap the end of the screwdriver or get to work with a bit of WD-40. I recommend once you’ve undone one of the two screws, to hold the cap down with your thumb while you undo the other, otherwise  the slide springs will try and push the Cap up and skew it, making it more difficult to undo the other screw. Lift the Cap off and gently extract the Spring, putting both to one side. You do not generally ever need to replace the springs. Now gently pinching the Black Rubber Diaphragm with thumb & forefinger, and working your way around the edge lift it up off the Carb Seat, out of the little Groove in which it’s in.. Then, using two hands, again thumb and forefinger, extract the Diaphragm vertically upwards. It will come out with the Black Plastic Slide attached and the Needle hanging out the bottom. When it’s free, grab the Plastic Slide and tip it over, pouring the Plastic Washer, Needle with E-Clip and Lower White Spacer all into your hand. The needle/E-Clips/Lower Spacer (Upper Left of Picture) should all come out as one unit, the upper washer separately. If you don’t know whether your bike needles have been altered, they should stamped 5E94 and the clip should be in the 4^th groove from the TOP (Blunt End) of the Needle. The Stock Needles are on the Left of this Needle Picture, Dynojet Needles on the Right. Check the needle for wear, score marks or an easily rotating e-clip in accordance with Factory’s Worn Needles guide. If all is O.K. Put them all in a little box for safekeeping.

• Inspecting the Rubber Diaphragm. NOTE: Do NOT spray the Rubber Diaphragm or indeed any Rubber Parts you wish to re-use with strong solvent. Some Carb Cleaners contain strong Solvents. Use a gentle soap like Dishwashing Liquid. After you’ve cleaned it, (you can leave it attached to the barrel), with your thumb holding the bottom lip of the Diaphragm, hold the Rubber of the Diaphragm up to strong light and stretch it by pulling upwards. It can take a fair amount of pulling. Work your way around the full circle of the rubber. If there are any splits or holes you should be able to see these fairly quickly and the Diaphragms should be replaced.

• Inspecting the Slides. If the Air Filter lets any gunk through or somehow dirt gets trapped in the Carb, the Carb Barrels can wear at the front (curved) face and at the Wings on the side, which results in their becoming scored, so check for scoring on these surfaces. They are fairly robust, (mine are actually quite scored but still function adequately), so you don’t need to replace them for a bit of scoring. Don’t forget there’s fair amount of Air Pressure against the back of the Slide, even if it doesn’t go up and down that fast. (It’s rate of rise and fall is controlled by a mixture of the Airflow through the Butterfly valve, the spring stiffness, the size of the little hole off-centre in the base oft the Slide and to some extent the friction caused by wear at the wing and front faces. There is no external mechanical Control on the Slide). That’s all you can inspect that comes out of the top for now. You won’t be able to get the Slide Carrier or the Carb Venturis out until after you’ve extracted the Main Jet.

• Inspecting the Float Bowls. At this point I’d recommend just gently screwing the Diaphragm Cap BACK on, but without any of the other bits you just took out. The reason is so when you turn the Carbs over and stand them on the Diaphragm Caps to remove try and remove the Float Bowl Screws, you have a stable end on which they can stand. The Float Bowl Screws are Very Tight and again you run the risk of mangling the screws. Again, you may even need to gently tap the end of the screwdriver or get to work with a bit of WD-40. In despair you can use a pair of Vice-grips and get some new Screws later. Don’t try heat except as a last resort (EXTREME FIRE HAZARD) and make DAMN sure the Bowls are DRY.! Many people have actually replaced these Phillips screws with Allen Screws and I’d recommend it if you intend to take your Carb apart often, for re-jetting or whatever. When you get the Bowls off they look like this on the inside: Float Bowl. Not much to do there, but give it a little cleaning and inspect the Gasket for cracks. Again, don’t use Harsh Solvents on the Rubber Gasket.

• Inspecting the Main Jets. What you should see now is something like this, except in the middle of this picture Main Jet Removed there is an  aluminium stalk with a hole in it where I’ve already removed the Main Jet. The Main Jet screws through the hole in the Aluminium Stalk which pokes up through the Float Frame. The Main Jet looks like this, Stock vs. DJ Jets, to the bottom left is the Stock Jet, to the right is my Dynojet Jet. Using the Large Screwdriver (Make sure it is good and WIDE so it just fits in the groove), undo the Main Jet and remove it. It should be stamped “132.5” if it is the stock jet. Check there is nothing blocked in the hole and if so use a stiff PLASTIC rod or Bristle, NOT a wire Brush Stalk, to dislodge the blockage. Put this aside.

• Inspecting and replacing the Float Frame O-Rings.  When you look down on the Float Frame, close to the idle mix screw location (Top of picture) you will see a plastic Stalk about 5mm in diameter which connects the Float Frame to the Carb Body. Grasp this stalk as low down as your fingers will allow and wiggling it a little bit pull it gently vertically upwards. It is quite tight until the O-ring comes out of the hole. When you pull it out you will also pull out the Float Valve, which hangs off a Metal Tang by a thin wire. The location of the Metal Tang it hangs off is marked up in this picture: Metal Tang. It’s O.K. for the Float Valve to fall off the Tang (and it probably will), when you remove the frame and I don’t think it makes too much difference which way around the wire goes because it’s centralised over the Float Valve, though you can make a note of it before you pull out the Float Frame if you wish. WATCH out the Float Valve doesn’t drop down the drain.!! If it didn’t fall off, tip the frame to one side and take it off and put it aside. When you get the Frame out you will see something like this: Float Frame. The Float Valve is still hanging off the Tang in this picture. The O-ring will look this: Float Frame O-Ring. This is the first of the two culprits of Flash’s Pukin’ Petrol Syndrome. You can easily replace this O-ring. Get a blunt needle and gently prise it off, then roll on a new one. (Size given above). The Carb Body minus the Float Frame and Main Jet looks like this. Float Frame Hole Location. The marked hole is the Float Frame Connection location. Shake the Floats gently to see if they have any petrol in them, if they do then they are leaking and need to be replaced. Some Web-Sites reckon if the Floats are discoloured they should be replaced, but I think they can be discoloured and work just fine.

• Inspecting and replacing the Float Valve Seat O-Ring. With the Float Frame removed, you will see the Float Valve Seat, which is where the Float Valve (that you just pulled out with the Frame) sits into. It is a Dark Brown Brass Cylinder. In the same way you just took out the Float Frame, Grab the cylinder and wiggle it out. At the bottom you will see the O-Ring, which can also be replaced. (Size given above). This is the second of the two possible culprits of Flash’s Pukin’ Petrol Syndrome.

• Inspecting the Float Valve. The Float Valve itself is tipped with a Rubber Pointy End which does the sealing into the Float Valve Seat. Inspect the tip to make sure it is not worn with a severe groove or the tip broken. At the TOP of the float valve, under the wire (which is bent into a loop) is a small piston. Underneath this piston is a VERY fine spring, which gets compressed when the Fuel Level push the Floats Up. Check, by tapping very, very gently, that this spring can be compressed and doesn’t “stick”. This piston and spring is discussed in more detail below, for checking the Float Heights, once you replace the frame. "One member said he fixed a problem by replacing the little cutoff valves AND the seats, for the Float Valve, as they weren't shutting properly, which means that even with the floats at the right height, he was getting too much gas."

• Removing and inspecting the Pilot Jet. With the Float Frame removed and the Float Valve Seat removed, all that is left to take out and clean is the Pilot Jet which is the small brass screw in the well just visible in the photo. (needs RED Circle!). Unscrew this with your small thin screwdriver, taking extreme care with the soft brass. You can easily ruin Screwdriver Slot. Tip the Carb over and let it drop out into your hand. It has holes in the sides as well the end and should be stamped “41.3” if it is the Stock Pilot Jet.. Check you can blow though it and all the holes are clear. Again use a plastic brush bristle to clear any obstructions, but not one from a Wire Brush. That’s all the things inside the Carb Bowl that need tending to. Now’s a good time to put it back in its little hole. One less thing to lose.! Screw it in until it seats then a little more. Just “FIRMLY”. Use the correct-size screwdriver or you will ruin the slot and burrs from a poor Screwdriver mangling pieces of the slot, could jam in the holes you just cleaned.

• Removing and Inspecting the Idle Mix Screw: While it can be done with the Carb Bowl done up, it is a VERY good idea to check the Idle Mix Screw with the Carb Bowl off and everything out. The reason is this. As you can see the 3^rd (and finest, hence easily broken) replaceable O-Ring is located on the Mixture Screw. If it wears out or there has been too much vigorous screwing of the Idle-Mix Screw in and out (sounds horrendous doesn’t it) bits of the broken O-Ring can get stuck in the little hole that allows fuel from the Carb Bowl, enter directly into the main Carb Venturi (NOT the Venturi JET) at idle. Unscrew the screw all the way out, check the condition of  the spring, the washer and the tip of the Screw. Replace the O-Ring. (btw the Washer in this picture, between the Spring and the O-Ring is NOT the original, it is too big, but the old one was missing at the time I took the Photos). It is hard to find the correct washer, because it is a very small diameter and not very wide, so try not to lose them.  The order shown is the order it gets installed. You can screw these back in now. Screw them down until they are LIGHTLY seated. Do NOT screw them up real hard, you will damage the fine tip. Then back them out 3.5 turns, with a screwdriver. This is the STOCK setting.

• Removing and Inspecting the Slide Carriers and Carb Venturis. With the innards of the Carb Bowl out, there’s nothing to break if you turn it over, so turn it back upright and undo the Diaphragm Cover again. Now that the Main Jet, which actually Screws into the bottom of the Carb Venturi Jet, is out, you can remove the Slide Carrier and the Venturi. Assuming your Diaphragm, Slide Barrel and Needles have already been removed, do this by grabbing the Grey Plastic Frame (Slide Carrier) and simply pulling it upward, out the Top of Carb. Don’t worry about the 4 Plastic Tabs at the sides they just pull up. If you don’t pull it out too vigorously, they will be just fine. When you pull it up, the Carb Venturi comes with it, because there is a Flange at the top of the Venturi, which sits in the bottom of the Slide Carrier. It should look like this:  Slide Carrier, Venturi attached. You can just push the Carb Venturi toward the top of the Slide Carrier to remove it. Underneath the Slide Carrier is an O-Ring, which gets compressed when you do up the main jet which pulls the Carb Venturi Down and hence the Slide Carrier O-Ring, onto the Carb Body. At the bottom of the Slide Carrier you will see the O-Ring, which can be replaced. (Size given above). Now check the Carb Venturi. The main hole, down the middle is large enough that it should never get blocked. However, on the sides, as you can see in the picture, are a number of small holes. Clean these in the same way as the other Jets, with a small NON-Metallic bristle.

• Replacing the Slide Carrier and Carb Venturis. Note that the Carb Venturi has a Flat Surface on one side, at the bottom. This flat surface sits against a Pin in the Carb Body, which you can see if you look down the well that the Venturi came out of. This surface sits against the pin so that the Venturi doesn’t keep turning when you screw up the Main Jet. Once you’ve cleaned the Venturi Jet and have replaced the O-Ring, put the Venturi Jet back into the Slide Carrier and press it into the small wall, so the flange seats. Note also, for Slide Carrier replacement, that the curved part of the Slide Carrier is at the FRONT or Engine Side of the Carb. Then turn the Venturi so that the flat surface lines up with the Pin. Smear the O-ring with a little oil and press the whole Slide Carrier/Venturi combo back into position, so that the 4 Tabs are all the way down. If the Venturi pin pops-up when you press the Slide Carrier in you haven’t lined it up properly, so have a look at the pin/flat side arrangement again. It should stay down OK until you get the Main Jet in position.

• Replacing the Needles, Springs and Diaphragm :Now’s a good time to put back the Slide + Diaphragm, Needle, Spring and Diaphragm Cap in that order. See Needle Parts Install Sequence. Before you start smear a little oil on the Diaphragm Seat and on the Sealing Ring of the Diaphragm, where the Diaphragm Cap seals it to the Carb Body. I find it easier to install the Needle (With E-Clip and Spacer Below it, on the Needle), the Upper Washer IN the Slide Barrel, keep the whole shebang in place with the spring and feed the lot into the Slide Carrier. If the needle comes up a bit pull the Slide Barrel out a bit and try again, keeping it as vertical as possible so that the Needle can drop into the Venturi. Thread the Spring onto the little green “Spring Guide” under the Diaphragm Cap. Press the Diaphragm into the Groove on the Carb Body and make sure it (more or less) stays in. It might try to pop out, but don’t worry when you put the Cap on it will slip into the groove, so to speak. So put the Cap on and slide it around a little bit on the rubber, just to make sure the rubber is down in that groove and you haven’t pinched it somewhere. Do up one bolt, just seated, then the other. Then Tighten both, nice and firmly, because they vibrate a bit, although damped by the intake rubbers, but not so tight you kill the head of the Screws. Now you can turn the Carb over to stand on the Diaphragm Caps and work on the Floats. For Problems reseating the Diaphragms see Diaphragm Trouble below.

• Replacing the Main Jet. This Part’s easy. You will see the needle where the main jet goes, so Screw the Main Jet into the hole by hand, making sure the Needle stays Central to the Jet. When it is fully in, Tighten it up firmly with your LARGE WIDE Screwdriver. Do NOT over-tighten, it’s soft Brass. Just Firmly, i.e. so it seats and then a little more. Remember you will initially be compressing the new O-Ring you just put on the Slide Carrier.

• Replacing the Valve Seat. Again fairly simple, just push it back in place, but put a little oil on the O-Ring first so you don’t ruin the Dry Rubber against the Metal Sides.

• Replacing the Float Frame. Replacing the Frame is fairly simple. First, smear the O-Ring with a little oil. Then, feed the wire loop of the Float Valve over the Metal Tang and position the frame over the Carb Body, with the Float Valve positioned over the Float Valve Seat and the Rubber O-Ring on the Plastic Frame Stalk over it’s hole. Push it into position. The Float Valve likes to fall off the Tang during this procedure, so either tip the Carb Body and hence the frame so it stays on, or use bit of bluetack to temporarily hold it in place. Here's a picture, with all three parts not yet in the Carb Body, (on it's side) of the Float Valve in the Float Valve Seat and attached to the Tang on the Float Frame.

• Checking the Float Height. Checking the float height is like a mixture between Art, Black Magic, Science, Witchcraft and Acupuncture. i.e. It’s a really, really hard measurement to make. Even more so without the right tools. Factory’s Site gives a fairly good description of the measurement plus they sell a Special Tool, also shown on that site. Like I said earlier the tool is a neat idea, but the workmanship, for the money, is terrible. Read their instructions first, then read on here. What they do NOT mention, at least on that page, is that the Float Bowl clamps the frame down and holds it in position (You might have wondered how it worked flopping around in there) to the Carb Body. It does this by clamping the two little plastic tabs that can be seen on the side of the Frame, in  the front of this picture. Float Tab On. You WILL need to hold these two down also (firmly), while making the measurement. Use a Bulldog clip, a Wife, a Girlfriend, a Son, a Dog, whatever. It must be clamped down to make the measurement. Make sure the Stalk with the O-Ring is also firmly in place. Now what you need to do is tilt the carbs so the floats swing out far enough that they do NOT compress the Float Valve at all, not even that little piston at the top I talked about earlier. Then slowly and gently, rotate the carb body back until the Float JUST touches, but DOES NOT compress that little piston on the Float Valve. Try it a couple of times until you get the “feel” of it. So now, holding the Carb in this rather awkward position, with your Special Tool or your ruler or your custom-made gizmo if you made one, measure from the Carb Gasket Surface (i.e. where the Float Bowl Gasket makes contact with the Carb Main Body) to the TOP of the HIGHEST Float. With the Tool SET at the correct measurement, the tool should just graze the top of the float. If it clears it by miles, your FUEL LEVELS at which the Fuel gets cut off will be too high and may be the reason for the rich sooty residue on your Spark Plugs. (Remember you are measuring the FLOATS upside-down, don’t get confused between FLOAT HEIGHTS and FUEL LEVELS. The HIGHER the Float Height i.e. what you measure, the LOWER the FUEL LEVEL at Fuel cut off!). To RAISE the Float Heights (Raise the Fuel LEVEL) you need to bend the little Metal Tang, shown in this Picture Float Tab On DOWN. Do this by hand, using one finger, a small amount at a time. Conversely if the first measurement you make forces the Float Down, it is too high i.e. the Fuel gets cut off too quickly (Lean) and you will need to need the Metal Tang UP. Remember small movements, when bending the Tang. Repeat until the measurement is right. Keep the beers on ice until after this procedure, you need steady hands. 
  
  Notes:

• 1. Flash notes the manual says to put the seam in the float parallel to the joint where the bowl meets the carb (Gasket Surface). For him, that was WRONG. The float level was too low (once the carbs were back right side up). It wouldn't sustain a speed over 80 mph. (The manual doesn't actually say that ed.).

• 2. Float Height. I discussed this with Flash at the time. Setting the float parallel to the Gasket surface is a rough measurement. From what I understand it's what he interpreted as the approximately correct setting from the Maint. Manual. I tried to pin him down, but he said he adjusted it following that approach and when it didn't allow him top speed he took them out again and bent the tang "a little". When I asked what height he says "I dunno", I bent it "a little". Anyway, there is a correct measurement and a correct WAY of measuring it. If you're like me, not too comfy with "a little", you measure it the right way. I put mine at 14.6. Several times. It worked FINE. At the end of the day, what Flash did was right, because he bent it just enough to get fuel delivery all the way across the board, without flooding at low rpms when the demand was not too high and with no overflow of gas because it could never shut off, when switched off. It's a TRICKY measurement, as you seem to know from other bikes. Marty #426 did note he went back to stock height, his floats WERE going too HIGH to shut off => his must have been about 12 too I guess. THAT makes sense, if the tang spring weakens due to float pressure, or the Plastic cage wobbles about. Don't forget when you measure it to HOLD THE PLASTIC TAB on the CAGE down, so it's firmly fixed. If you replace the O-rings on the cage, seat it properly first before re-measure. No cats were harmed while rebuilding my carbs ;-)

• 3. My Description vs. Factory Website Description of the Float Bowl Measurement
  
  This FAQ Says:
  
  "Now what you need to do is tilt the carbs so the floats swing out far enough that they do NOT compress the Float Valve at all, not even that little piston at the top I talked about earlier. Then slowly and gently, rotate the carb body back until the Float JUST touches, but DOES NOT compress that little piston on the Float Valve."
  
  Factory says
  
  1. Tilt the carbs so that the floats just flop over towards and into the carb body.

  2. Tilt just enough to touch and close the float the float valve, but...

  3. Do NOT compress the float valve spring when measuring.

  4. With the metal adjustment tang on the float just touching, but not compressing the float valve spring, place the Setting Gauge over the highest part of the float. If there is a gasket or o-ring stuck to the carb body, remove it while measuring.
  
  The Factory Website and the FAQ actually say exactly the same thing, however they do not clarify how sensitive that little piston is. I found it easier (with the floats already flopped over toward the carb body) to tilt the floats away from that little piston, then tilt the carb so they go back into the body until the tang just touches that little piston. Performance could be saying drop them into the body (compressing the piston) then tilt the body so they come out SUCH THAT the piston is not compressed. However I believe by saying "... floats just flop over..." they are saying the same as this FAQ.

  NO the valve is not open during the measure it is STILL closed. It ONLY opens when that little wire on the tang pulls the whole valve up. As long as the tang is not pulling up on the valve it is closed, under it's own weight (gravity...). What you have to remember is that valve is up the other way, normally, so what the little piston does, because it is spring loaded, is work against the valve pushing it up to close off the supply to the bowl.

• Replacing the Float Bowl. Smear a little oil on the Gasket, making sure it is seated properly in its groove, then replace the Bowl and do up the Float Bowl Screws. Allen-Head screws are a good replacement.

• Repeat from “Inspecting the Carb Needles” down,  for the Second Carburettor.

Diaphragm Trouble

Diaphragms don't go back into place after lifting off the Black Covers?

I lifted the diaphragm covers today in order to check the diaphragms and needles out, as I've been getting rather few mpg. I have no idea when the insides of the carbs were changed out the last time, but I guess it's probably been done since the bike's got more than 62,000 kms on it. The needles looked brand new to my (untrained) eyes though. So did the diaphragms, and thorough checking revealed no rips or punctures of any size or kind. HOWEVER, I did get a bit puzzled over the fact that my diaphragms are way too large to fit in the circular indentations they're supposed to settle in before you screw the covers back on. (They were indeed pinched under the covers by whoever screwed them back on previously). I've checked the FAQs, but I only found this (from the carb cleaning faq):

"Press the Diaphragm into the Groove on the Carb Body and make sure it (more or less) stays in. It might try to pop out, but don’t worry when you put the Cap on it will slip into the groove, so to speak. So put the Cap on and slide it around a little bit on the rubber, just to make sure the rubber is down in that groove and you haven’t pinched it somewhere. "

My problem is that it is positively impossible to get the entire edge of the diaphragm into said groove. My diaphragms are at least a couple of millimeters too large (across) to fit, and after 45 minutes of trying to get the edge to seat in the groove all the way around, I gave up. I had to screw the covers back on, pinching both diaphragms in the process. Looking from above, either diaphragm would protrude from under its cover for maybe a fifth of the total circumference.. this can't be good. Has anyone else experienced this problem? Could it be that whoever replaced the diaphragms before me got the wrong size? In your experience, is the diaphragm exactly, or at least almost exactly, the same diameter as the groove it's supposed to sit in? I mean, this was NOT a case of the rubber "trying to pop out".. I can't see how anyone could have managed to get the entire edge down there, let alone keeping it down while reaching for the cover. Last question: could this be (part of) the reason why my mpg is low? I'm imagining that pinched diaphragm edges could be fairly equivalent to rips in the rubber. No, there was nothing sprayed on them. Also, they were already pinched before I even started unscrewing the covers, so the previous attempt to get it right apparently failed, too.

I called the dealer today. It appears to be a well-known issue with older diaphragms, they simply grow larger with age, due to contact with gas fumes. The mechanic I spoke to thought my diaphragms are the original ones, which would make them almost nine years old. (They are approximately three millimeters too large, across.) He also said getting older diaphragms back in the slot is a major PITA. They wanted $18 per diaphragm (must have remembered the price of some other part), so I called the local Suzuki shop for a quote of the GS500 diaphragms... which were priced at almost $40. So I ordered them from a BMW car dealership instead, saving $2 compared to the bike shop.. guess I'll use my savings and buy a snow cone or something :) Emil '94 F650 -- Malmö, Sweden.

• Sound too big to me. I had the Tank off and the Diaphragms out on my Classic over 20 times to swap needle positions while rejetting. I wrote the above description and it was exactly like that. It didn't fit EXACTLY, but a little oil, lightly pressing down with the plastic cover and rotating, it popped back in just fine. Sounds like something amiss there. They may have installed the diaphragms off a different carb. The Suzuki GS500E ones may fit though, if you need a new set. What you could do, if you want to check, is to take them out, flip the rubbers over and dab the oily lip onto a piece of paper (or just take the whole thing) to the dealer and ask to see a replacement if they have one in stock to measure it. Do the same at the Suzuki Dealer (See FAQ for Suzi Part No's) and ask both the price. k.

• If you happened to be spraying carb cleaner (or equivalent) and it got on them, they can swell up larger (at least the ones on my Airhead did). Let the solvent air out of them for a day or two, they may shrink back (if they're not already trashed by the forced installation). If not, I agree that they sound too big. Marty #436-Chicago-97 F650F

• Secondly as someone else complained, once I came to refit the diaphragms they wouldn't go - at least 3mm too big. Don't worry they will still fit. The secret is lots of fine (sewing-machine) lubricating oil. If you lube the grove on the carb body and the lip of the diaphragm. Working with both hands from a point on the circumference feed the diaphragm lip into the grove. Then moving your hands in opposite directions around the circle keep feeding the lip and press each section lightly back towards your original starting point. The idea is you are compressing the rubber lip to a smaller circumference. The oil will help the already seated material slide in the groove. Once I did this my impossibly large diaphragms went back on without any problem. The oil helps hold them in place whilst you reach for the cover as well. Hope it doesn't rot the rubber! Simon in Ireland.

Q. How Do I Replace the Carbs.

A. With Difficulty, Patience, Cotton Gloves and Vaseline.  

Putting them back can almost feel more gruesome than taking them out. You think your ruining something, but the rubbers are pretty hardy and with a bit of patience you’ll get there. I suggest you use some of the lubricants Flash mentions on his removal procedure or coat the inside of the rubbers (Both Airbox and Engine Side) with Vaseline. Reconnect the Choke Cable BEFORE you start pushing the Carbs in (You can do it afterward but it’s very hard to get to the plastic nut.) Again, please, do NOT over-tighten the Nut. It’s just Plastic! The Throttle cable can be reconnected after you get the Carbs back in, but you can do it now to save yourself the trouble. Affix the Wire-Head to the Throttle-Plate then twist the throttle Plate (or pull the wire) until there is enough slack to get the bend back into it’s mounting. Work the Carbs down into the cavity, again pulling back the softer Airbox-side rubbers, to fit the Engine Side first. After you get the Carb ports mounted into the Engine Intake Manifold Rubbers (They are stiffer and relatively easy), the Airbox side rubbers will probably still be all squished up. Try and free the bottom first and get them fitted to the Carb, then with a finger or BLUNT instrument (e.g. Flash notes a Tyre Iron works well), working from the sides towards the top, stretch the rubbers over the Airbox Side Intake Ports. These Ports are not that wide, only about the width of the Steel Hose-Clamps, so after you get them in place pull the whole assembly Horizontally BACK toward the Airbox so you know they are as far on as they can go. THEN do up both sets of clamps, lining the clamp heads up so they are easy to access with a screwdriver.

Replace the Tank Seating-Plate, making sure the choke and throttle cables drape OVER the top of it and they are free and not caught anywhere between the Carb and the Throttle on the Handlebars. Replace the Tank as indicated in the Gas Tank Removal-Replacement FAQ.

That’s it.! Sounds long and arduous, but in reality it’s not, I just wrote a lot of detail. I can get the tank off, whip the Carbs out, change the Jets and Needles, put it back and get the Tank back on in about 45 minutes, during my lunch hour and still have time for a sandwich. But I’ve done it way too many times. I’m not suggesting you should hurry through it though, take your time. A job worth doing is worth doing right. It’s a job you can do in a few hours over the course of a leisurely day.

Any comments on the FAQ, improvements or suggestions, drop us a line. For all you poor people with F.I., aren’t Carbs FUN.!

Thanks to Flash and Todd, who always manage to be both entertaining and informative, to Mark for getting out there and doing it and to Craig, Tom and the other guys who went and are still going crazy trying to get the jetting right, having pulled their Carbs for the umpteenth time. Big thanks to Mal for his great close-ups of the Float Valve.

Note.: I have no affiliation with Factory Pro who are mentioned often in this FAQ, though they do have some very good tips. They didn’t like it when I started asking questions about their jet kits without buying it, but hey if you can’t ask about something they want to sell ! Others have had a good experience with them and find them helpful.

Cheers & Rgds

Kristian

Is there any way of Setting/Checking the Float Height with the Carbs ON the bike?

by Richard #230

The Downtime Files of the April issue of Motorcycle Consumer News has a really great tip for checking float level height without removing the carbs: Connect a piece of clear tubing to the float bowl drain tube, bend the tubing up against the outside of the float bowl and turn on the float bowl drain screws. The gas will rise in the tubing and you can take your measurement by observing the top of the level of the fuel in the tubing, as it will rise to the same level that is in the inside of the float bowls.  The Classic has bowl drain taps on the bottom of the float bowls that you can hook up a plastic tube to. The only problem would be finding clear plastic tubing that will fit tightly over the drain nozzles. I think you could find this tubing in a pet fish store. If the tubing was a bit large, you could use wire wrapped around the tubing and twisted with pliers to compress it over the nozzles so that the fuel wouldn't leak while you were checking the float level.

The best way to use the tip is to check your float level when the bike is new, or at least running well. Place the tube on the float bowl drain and then turn on the bowl drain tap. Wait until the level stabilizes, then scribe a mark on the bowl for future reference. Then in the future, if you have a carb problem, you can perform the test again and check it against the mark. If it is higher than the mark, then you might have a leaking float or bad float needle valve.
 

• You know the original Kawasaki Z-1's had a tap on the bottom of the float bowls and you used a device just as you described to check the float level. I don't know where you would tap the float bowls on a Classic or if you would have small enough hands to connect it but this is a tried and true method that has been around for a long time. F650GS Dakar, Oregon. Steve 1130 Or

• <<My question is, once you can see the fuel level from the outside of the carbs, how do you know it's the correct level? Is there a reference mark outside the carb? >> Nope. The only real way to measure it is from INSIDE, See here: http://faq.f650.com/FAQs/Carb_Clean.htm

• Only a few carburettor makers (and then mostly for racing carbs) give fuel level info. The most common tech info is the height of the bottom of the float(s) relative to the bottom of the carb body with the carb upside down. BUT- when the float height is absolute right (upside down), reassemble the carb and take an accurate measurement of the fuel level, hose attached. make your own mark(s) on the carb body and then you use that marking(s) the next time you want to check the float height. Whenever "something" (being it a piece of machinery, boy/ girlfriend or whatever) works near perfection, ALWAYS make a note of ALL information you have and can get with regard to whatever it is. Motorcycles: Fuel level or pressure, ignition timing or map, valve timing (valve movement relative to degrees of crank rotation), compression pressure (with info of battery voltage or rpm of engine), and so on. The more info of the "perfect" machine you have, the easier it is to find any fault WHEN (it will not be "perfect" forever) you want to restore it to it’s former state. Haakon#626 (Norway, F650GS)

Carburettor LINKS                                                                                                                              

Some good  resources for Jetting and Plug Reading Information - Not F650 Specific.

Opinions (On Carb Cleaning/Particular Parts Replacement).

Some of the comments below might seem to indicate the 14.6mm measurement is no good. But if it is measured properly, I believe this measurement is fine. At present there is just not enough feedback to say either way. So set it stock, measuring it right and if it doesn't work for you, (runs outta gas at HIGH rpm/flat out speeds), LET US KNOW!

• The 99 model's carburettor is specified to be set with a .56 inch clearance from the float bowl face. I used those exact specs and had the bike stall from insufficient gas in the carb. after a brief time the bowl fills enough for another short distance. I've set it down about twenty percent lower than this spec but has anyone else had trouble with performance attributable to setting the float bowls to this much of a gap from the measuring surface. Unknown

• I've been working on my bike since the last posting of my problems (carbon fouled plugs and rough running). Done so far: 1. Lowered the needles, which made the bike able to run at lower rpm in the same gear and only a little bit of carbon fouling on the spark plugs. 2. Changed the chain and sprockets, which made the bike run at a stable speed on a constant throttle position (smooth is the word). 3. Changed the Spark Plug Caps to OEM 1kOhm (had NGK 5kOhm), this made the bike run at even lower rpms in the same gear (and perhaps a little bit smoother). I measured the Resistance before the change to 14kOhm and after to 10kOhm which means that the current is now 40% higher at the spark plug cap. I took the bike out for a 50 miles spin this afternoon and the bike runs pretty good now - no rough running, good rpm-range in gears and easier starting. Could it run even better? - I have no idea since I have no other bike to compare it to. Problem left: The needles are 1 position lower than they are supposed to and the bike is still a little rich - not much though. Solution: Next thing up is to remove the carbs and change the emulsion tube, and while I'm at it I'll change the main and idle jets (all parts laying on my desk). I'm going to try to measure the float height also. If I ain't mistaken mine (Idle mix screws) are set to 3.0 (or somewhere near). I did a major overhaul of the carbs last spring, which included new Venturis, 135 main jets and new OEM spark plug caps. Since then the bike is consuming approx. 15% less fuel and the spark plugs are no longer carbon fouled, actually they look brand new. 60.000 KM F650 1995 Spakur in Sweden #1117, '95F.

• I was just reading the carb cleaning FAQ, and perhaps you could add to my comments at the bottom of the FAQ that my float heights were off by ~1.5mm (too low) and that after these changes the fuel consumption is now 15-20% lower.

• Woooohoooo!! 55mpg!! How many miles were on the bike/carbs when you did your rebuild?. 28.5k miles. What year "classic"?. 1999. What kind of environment has the bike been stored in when not in use? Outside but covered, in the mild Seattle climate (i.e., never super hot nor frigid cold) How often did you or someone ride it? At least weekly, except for last winter when I put it up for 12 weeks (using proper storage protocols, drain carbs/tank, etc ...) all kinds of use: city commute, touring, some dirt roads. The precipitous decline in mpg occurred while on my 13k mile trip this summer. NormJ #473.

• Here, so far , is the sequence of events.
  March '02 - removed Ron Woods "muffler" replaced with stock. No other mods. Bike runs rich, but otherwise well.
  July '02 - inspected carbs for presence of DynoJet kit. There was one, I dropped the needle on that kit to see if it would lean out my mixture. It did, but not enough.
  Aug '02 - replaced all DynoJet bits and bobs with stock carb parts. Also replaced K&N air filter with stock. Too early to tell if fuel economy has improved (it wasn't all that bad before) but now that I'm back to stock here's what's happening. Throttle response is better at low RPM (It would tend to bog if I sat at idle too long and then went to take off - you like at traffic lights). Plugs aren't fouling any more. I am now going to restrict the airbox so it's as close as I can get it to stock to see what happens. That's about all guys. I don't know if there's anything there at this point that merits an addition or change to the FAQ. I will say that moving the hose clamps as far back on the rubbers as possible makes all the difference as far as insertion and removal. And clumping cat litter makes a great absorbant for gasoline spills or draining the little hoses. Sean #1015 Ottawa Canada.

• FINALLY rebuilt those carbs (@26K). Surprisingly, the needles and emulsion tubes looked good (replaced anyway, stashed the old ones for spares). Both diaphragms had small tears, both idle mix screws were only 2.25 turns out, and both floats had to go WAY too high to shut off flow (float needles were well grooved as well). Here's hoping that the changes back to stock will improve my gas mileage significantly (running 30-35 MPG at last check, boy did I miss my Acerbis tank...which is ALSO repaired now). Maybe that 17-tooth front sprocket won't feel so tall now! Marty #436.

• Note to all who helped me with advice on returning the carbs to stock (Kristian#562; Todd #389; Richard #230; Shank NYC; Teddco #1192; JAMES) We did it yesterday (with the exception of Dyno jet springs) and it runs really great now. No flat spots or roughness in the acceleration curve. We screwed up on the springs, but we can probably pull the diaphragm cover and switch out springs without pulling the carbs. Somebody tell me that can be done. Pulling the carbs was not that hard but certainly not easy.  XtreemLEE#1188.

• Carb removal experiences. I removed the carbs today, using the "mild force" method described in the carb cleaning FAQ (i.e. no airbox removal). Everything went ok, except that I wasted one of the float bowl screws. Had to get a screw extractor to fix it. d*mn that screw was hard to undo... Anyway - when reinstalling the carbs, I ran into a problem. It wasn't that hard to get them into the engine side rubbers, but then I found the airbox side rubbers were suddenly way too short... there was a 2 mm gap between rubber and port on the airbox side when the carbs were fully seated in the engine side rubbers. Apparently, the rubbers had been pushed into the airbox when I struggled with getting the carbs out. It was NOT easy to pry the rubbers back out of the airbox. Just a small warning and a note to self to take it a bit more easy next time. veggie deluxe, Sweden.

• Yep, changed both my diaphragms out last fall (both had failed). Bike exhibited the same drastic drop in gas mileage. Marty #436-Chicago-97 F650F

• Numerous problems this month (blown fork seals, poor pick up, worn head races) but all easily resolved with the help of the Technical FAQ's. God Bless You All.
  The poor pick up has been traced to the carb-mounted inline fuel filter but whilst I had the carbs out I decided to clean them anyway and have the following snippets to add to the FAQ. Firstly as with many others I found the float bowl screws difficult to budge - solution = get an impact driver, it does the job! Secondly as someone else complained, once I came to refit the diaphragms they wouldn't go - at least 3mm too big. Don't worry they will still fit. The secret is lots of fine (sewing-machine) lubricating oil. If you lube the grove on the carb body and the lip of the diaphragm. Working with both hands from a point on the circumference feed the diaphragm lip into the grove. Then moving your hands in opposite directions around the circle keep feeding the lip and press each section lightly back towards your original starting point. The idea is you are compressing the rubber lip to a smaller circumference. The oil will help the already seated material slide in the groove. Once I did this my impossibly large diaphragms went back on without any problem. The oil helps hold them in place whilst you reach for the cover as well. Hope it doesn't rot the rubber! Just the new head bearings left to install. My wife hasn't found the steering stem in the freezer just yet but I am not sure how I will heat the new bearings in our oven without her noticing! Simon, '98 F650, Ireland.

• To make a long story short, I am moving and all my tools are packed. I have a 2 month old new to me 1998 f650 with 22k. It started running poorly, died in the middle of a ride. I dropped it off at the BMW shop and they immediately want to rejet it as the plugs were fouled. No attempt or offer at idle mixture, etc. Re-jet was their only offered option. The bike is from the same altitude as my current town. I admit my ignorance as I have never owned a BMW, and don't really get this two carb hi/low with the F650. Are those guys trying to pull a fast on me?. Flash "That sounds like one of two things, you probably have either ripped carb diaphragms or else bad spark plug caps. Oh... might you have gotten some bad gasoline? Rejetting it is horseshit. You can check and/or fix either the diaphragms or plug caps yourself by using the FAQ" Sante Fe BMW treated us well, clogged idle jet was all it took. Chicken little '98 F650, Albuquerque

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Detailed Feedback: on Carb Reconditioning

• Feedback#1

Feedback#1

Rejet of the 97 F650 Carb with Tech Tips/Problems/Tools/General Whining

by Langlois

First: Get your airbox out...see the F650 Faq, remember to take the muffler off, much easier with it out of the way. I struggled for a while and could not get the angle right to pop it out without the pipe removed (the headers stay, the muffler is removed with the cross-over/connector pipe). NOTE: You do NOT need to remove the Airbox. Just pull the Carbs (ed).

Second: Have a cup of coffee, I am sure you just spent half an hour dicking with this and you will need your wits about you for the rest of the job!

Now, see photos:

Finally, I cannot recommend the guys at http://www.factorypro.com/ enough, these guys saved my butt. (the SS screws and jets are nice too!) But, saying that, jets are jets...you can buy them everywhere (almost) it's the service you need during and after the sale, they most certainly provided that!

Identifying a Float Valve Problem

See PUKING PETROL