Pipes & Rejetting (Performance Mods - Classic F650)
compiled, written & edited by Kristian #562; updated by Scott, ID #1244
Please read the Disclaimer before attempting any work in this FAQ.

If you're looking for GS Info, see GS Performance Mods.

If you're looking for Carb/Jet Tuning using Plug Chops, see Plug Chops in the Spark Plug FAQ


For Specific Performance Settings for various pipes and Jet Kits refer the Exhaust Rejet Spreadsheet and the JetKit FAQ.

For Details of Carb Removal and Dismantling, refer the Carb Cleaning FAQ.

For Air filters refer the Aftermarket Airfilter FAQ

Snorkels & Organ Pipes

Airbox & Organ Pipes General:


On the Pre-GS F, the Snorkel is the rubber Air Intake Funnel located on the RHS of the Bike to the rear of the Airbox, in front of the Coolant Reservoir.
You need to take off your RHS Side panel to access it. It looks like this:


Intake Snorkel

There is also an intake modification you can do on the pre-2000 F650GS, by letting more air flow into the Airbox via a couple of holes in the TOP of the Airbox. It only makes sense if you have a free-flowing aftermarket pipe, which the Staintune with a Baffle in is NOT, because thereís not point in letting more air in if you canít get it out the pipe fast enough.

The remnants of holes used on pre-96 F's can be seen by lifting the Seat and at the rear of the Airbox (on top), behind where you'd expect the filter to be are two circular depressions. These are actually plastic (non-removable) plugs leading to two different length vertical tubes (hence the name Organ Pipes) leading into the Filter Chamber. I believe the different lengths were to do with airflow or something but don't really know for sure.The pipe can also be viewed when removing the filter and looking inside. Here's a '95 Airbox, from Mal #1011. You can plug them like this.


Anyway, with a freer flowing pipe, you can let more AIR into the system by CAREFULLY drilling the plugs out. If you want to drill them out and leave the pipes IN PLACE start smaller than the outer limits of the depression, about 23mm. Otherwise if you drill a BIG hole you will also take out the pipes, not that I think itís a problem, but perhaps they made them that way for noise or airflow requirements.


This will LEAN the whole system out, so I would NOT recommend it without Rejetting. Rejetting can be a PITA so think carefully.! It will also suck your Mileage. If you're happy with it as it is leave it be.!


Hereís a view from the TOP. Organ Pipe Locations. I drilled mine out, but am currently experimenting with blocking them for fine-tuning my jetting.


About your comments, and about the organ pipes in the air box, BMW claimed less noise during the intake of the air by closing the organ pipes. My bike came with them open, and from 1997 the euro bikes came with them closed. Comparing, bike to bike, my bike with another of a friend of mine, I don't appreciate any difference in the intake noise. For me, the main objection can be made to open organ pipes is the care you must take avoiding water entering in the air box, mainly when you are washing the bike. And the advantage comes when you can watch trough them to see the inner part of the air box. By the way, the drain tube of the airbox is located in the opposite side where would be (right side of the bike), because when the bike is on the side stand the water tends to go to the left side and remains in the bottom of the air box. You must incline the bike to the right side to drain the water properly. I think this is one of the main (and fortunately, scanty) mistakes made in the design of the bike. I think this is the main cause the water goes into the carburettors, and by this reason they must be drained sometimes. Fede (Spain)


btw DO NOT Plug them unless you rejet your Carb to the Post '96 settings, which is possible, quite cheap and perhaps a good idea if it rains a lot where you are. Refer the Carb Clean FAQ for differences in Jet Settings pre and Post '95. You MAY thus be able to recondition your carbs, replace the Main Jets (and any other you need to Change) with smaller ones, replace your O-rings and Venturis, maybe also needles and Plug the Organ Pipes (Couple of LARGE TEST Tube Stoppers or Champagne Corks - See FAQ) and get better Gas Mileage, all at the same time. If you don't know what you are doing however, you might make it run like a real dog. Y.M. WILL. V.


Airbox Trimming

by Langlois

Andy's Airbox Trim Job! Rejetted. D&D Exhaust. Needed foam filters.






Oiling the Uni Foam Filters!

Plugged vacuum lines/Foam Filters/open airbox!

Plugged lines again!

Installed airbox

The Carb Tuning Range


Q. Which part of the throttle range is affected by what part of the Carb.?




Dynojet Recommendations on their Jet Kit


We recommend 2 turns out on the mixture, because we found that to work best on that bike at idle and off idle.  The float level needs to be set to the stock setting that is recommended by BMW.  We do not alter those settings in the kit.  That kit is only for up to the 97 model years.  We have not done any testing on the new model years.  I am not sure if it will work or not.  In some cases it is possible that you need to go back to the stock slide lift springs.  We designed this kit using one of your bikes, and the new slide springs improved the throttle response.  In order for this kit to work properly, you will need to remove the snorkel and leave the rest of the airbox installed.



Dynojet Research






-----Original Message-----

From: Kristian

Sent: Monday, July 23, 2001 6:42 PM

To: bmwtech@dynojet.com

Subject: BMW F650 Kit




I just ordered a Stage 2 jet Kit for my 1996 BMW F650.  I read with interest your page on the jetting. I have a Staintune pipe, Organ Pipe Holes drilled out in the top of the Airbox, Stock Filter, Snorkel in Place. Before I install it I have a few questions:


1. I was wondering why you recommend just 2 turns out on the (Stock) Pilot. That's very lean, particularly with a new pipe.

2. Have others needed to adjust float bowl settings with this particular kit. ?Do you have any recommended Float Bowl settings

3. A friend of mine has a 1998 F650.  The Dynojet page only lists the Kit for the 93-97 F. Can the same kit be used on his bike or are your kits not applicable.? Is it perhaps the kit was put out in 1997 and you just haven't changed the page.?

4. Another purchaser of your kit (1997F)  with a REMUS pipe, said that the Dynojet Springs were too stiff on his bike and caused a stumble in the mid-range 3800-4200 rpm. Has there been any other feedback from users of your jet kit for these bikes.? Has anyone else had to replace the Dynojet springs with the stock springs.?




Fine-tuning your Jetting
by Kristian #562


IF you're happy with your Emulsion Tubes and Needles, you could lower the needles one notch to lean it then add a Shim, just a thin small washer that fits the needle, placed under the e-clip, to raise it that half notch. The end-effect is you've dropped the needle a half notch.

Rejetting & Aftermarket Pipe Responses

Below are a number of (often conflicting) reports of Jetting from various modifiers. Your best bet is to see the Exhaust Rejet Spreadsheet for what exact settings people have used and their results. The opinions below are interesting, if nothing more than to show just how difficult it really is to get it right.


Adventure Pipe





Ron Woods


Rotax BMW, Direct Link: BMW_F650



Staintune Installation


The Staintune slips on over the end of the old header pipe. Just Remove the Rear wheel, Remove the LARGE heat guard off the old muffler, remove the LHS Cover, remove the old Muffler, put the crossover pipe of the Staintune over the old header pipes, bit of wriggling and some graphite may be required, but it does just slip on. tighten Crossover retaining bolt. Put the end can on the new crossover, Allen Key it tight only AFTER you have aligned the two retaining bolts of the end can. Replace Large Heat Guard. Start her up. Apologise to your neighbours if you finished this at 3 a.m. Time to do: 1 Hour MAX. Note some have had REAL problems getting it to fit. ed.


Hereís a picture of the Staintune on my ex-Classic: Staintune End Can, Staintune X-over Pipe. k.

Cracked Exhaust Pipe Welds


Ron Woods:







Dynojet Charts

Aftermarket O2 Monitors
by Tom #981 (Draft)

Air/Fuel monitors: I've done some more research

Here's what I sourced for the project of adding an O2 sensor/ air/fuel meter on my 97F:

A/F Gauges:

Here are also some other A/F, O2 links, although I've got a better list somewhere.


Rejetting Links

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

1. FactoryPro

http://www.factorypro.com General NOTE that the Mikuni-Sudco manual actually

http://www.factorypro.com/tech/carbtun.html Tuning CV Carbs recommends tuning the circuit from the Pilot upwards as they say each circuit is additive. I cannot put copies of the information on this site as Sudco has a copyright on this information. It's about a 13 US$ Manual from Sudco.


2. Nightrider


www.nightrider.com (Note: Actually for Harley V-Twin with CV Carbs, but general information is useful)

http://www.nightrider.com/biketech/carb_jet_ranges.htm on Carb Circuit Ranges

http://www.nightrider.com/biketech/carbadjust.htm on adjusting the Carbs

http://www.nightrider.com/biketech/hd_cv_mods.htm on Harley CV Carbs Mods

http://www.nightrider.com/biketech/hdcvcarb1.htm on Harley CV Carbs Mods

http://www.nightrider.com/biketech/hdsparkplugs.htm on Spark Plugs and Spark Plug Reading

http://www.nightrider.com/biketech/spkplghnbook.htm on Reading Spark Plugs, with colours of Plugs

3. Dynojet

http://www.dynojet.com/motorjet.shtml on Carb Circuits in general

4. The Chain Gang

http://www.f650.com on F650 in General - Excellent Message Board :-)

5. Detonation

http://www.factorypipe.com/Technical/Tech_Articles/Deto/deto.html More Detailed information on Fuel Detonation

6. Diagram of Overlapping Carb Circuits - See Diagram under Needles & Jets


7. Horsepower Calculator


8. Altitude Adjustments