F650 Idle Mix Screw FAQ

by Kristian #562, 12 September 2001
Please read the Disclaimer before attempting any work in this FAQ. Last Updated: 13 June 2006, by Winter #1935

• Where is the Idle Screw?
• Where on Earth is the Idle Mix Screw?

Other Related FAQs:

• Carbs Misc. FAQ
• Carb Cleaning FAQ

To the LHS of the LH Carb, it is a flexible "Wand" that sticks down, with a spring wound around it, about 2 1/2 inches long and sheathed in rubber (sounds kinky doesn't it), with a knurled knob at the bottom end. It is nestled close to the Preload knob.

Here, in the red box is the upper art of it. Idle Screw Location (Sorry, no pic of it ON the bike).

The Classic F Idle Speed is 1300-1400 rpm.

Where on earth is the Idle Mix Screw?

Here: Idle Mix Screw Location

The Idle Mix Screw (Circled GREEN) is under the Black Plug (if it's still there), in front of the Carb Float Bowl and under the Carb body. This is the LHS One and is accessible from the left of the bike. The other one (of two) is accessible from the RHS of the bike. The Manual says # of turns OUT from LIGHTLY bottomed out (i.e. screw in clockwise until just seats) is 3.5.

The Screws Circled RED are the Float Bowl Drain Screws, for emptying Crud/Water out of the Carbs.

A SkewDriver or similar tool is highly recommended to access these screws. Let's face it the screws aren't exactly hard to turn just hard to get to. Actually I have the Weekend Pro Model, DSK-1200, (I didn't buy the 12-Pack btw, just the one...) You really don't need anything else and the little handle thingy under the SC-1600 just gets in the way and leaves you LESS room in what's already a tight spot. Especially on my Ohlins Preload Handle Side. The SC-1600 might fit but I'm happy with the Standard Bevel. 10.95 too, if you can find it a Hardware Store. See SkewDriver.

Alternatives to the SkewDriver/SkewDriver Feedback

• Another alternative to Spectools is a tool from Harbor Freight. Cost is $8. I haven't used it (haven't received it yet), but you can see a picture and the contents of the kit at www.harborfreight.com, enter the number below in the "find item number" box. Part number is: 34273-3VGA. If you order $50 or more from HF, you get free shipping. Unknown.
• At a pinch you can use a bent Bobby pin. My rubber plugs are missing, but I found that the screws weren't stuck. I had used 10 different sizes of small screwdrivers and none of them worked. Then, in an overnight revelation, I decided to look in the BMW tool kit for a "special" tool even though adjusting carbs probably isn't considered a routine thing to do. There was a bent bobby-pin in the kit (I'm sure it wasn't from BMW) and it worked perfectly. Fit right in the hole and in the slot exactly. Turned the screws with no problem. I think it would be worthwhile to put the bobby-pin idea in the FAQs. Thanks again for your help. I will look for some rubber plugs so the screws don't get gummed up in time. William-USA.
• What's that? Bobby pins were used by women to keep their hair in place. They sort of look like thin black paper clips. They were sold in 5 & Dime stores for about a penny each and tended to end up at the bottom of every drawer ever accessed by a woman. I believe that they started losing favor as hair holding devices in the 1960's. However, I as willing to be corrected by the actual users of such devices. Richard #230, Pacifica, CA
• Geez. It's bad enough I admit to using a girlie item, but it's worse when I find out I'm old enough that hardly anybody knows what I am talking about. Richard got it right. However, the more expensive, high tech bobby pins were brass in color and stronger than the black ones. Evidently, I am lucky enough to have the high tech variety. I went by a bike shop today and they had an Keihin FCR Carb Wrench Kit distributed by Motion Pro Quality Tools and Controls (made in Taiwan, of course). Model # is MP# 08-0181 for a whopping $13.00 US. It has a carrying case and 3 adapters that can be inserted into a knob for easier carb adjusting. It only has 1 size of screw-driver adapter, but I bought it anyway and if it fits at all (I may have to grind it a little) I will keep it. William-USA.
• Just took my carbs off to replace cracked inlet manifolds today. Thought I'd follow the advice of the FAQ and check the idle mix screws, but they won't turn at all. Has anyone else come across this problem? I'm trying to cure excessive backfiring and have already tried increasing idle speed but to no effect. I know the idle mix screws are supposed to be 3 1/2 turns out from closed, but I can't check this. Does anyone know the depth the screw should be in the threaded recess? Not sure whether to just refit the carbs and see if the inlet manifolds have cured the problem. Ed UK
• I don't now the depth, but last year I couldn't turn one of the screws either. After trying myself I left it to a MC garage who worked on the screw for 30 minutes before it came out....bought a new one and installed it. Nowadays I try to work them out once in a while (every 3 months or so). If its stuck it probably means that it has been so for a long time, so if your problem has been noticed recently. Spakur in Sweden #1117, '95F.
• WD40 and patience should get the screws loose if you get them out undamaged I would use anti-seize on them mike410 (Iowa).
• You also need the right size screwdriver. One with too wide of a shank can get stuck in the tube leading to the screw and feel like the screw is not turning, when it is really the screwdriver that is not turning. I had to take my small screwdriver and file its sides down before it would fit all the way into the recess, without binding. Richard #230, Pacifica, CA
• SkewDriver Forever! ...and that may be how long I need to keep it in order to get any more use out of it. I ordered a SkewDriver from Spectools.com and it's perfect for adjusting the low speed carb jets on my '99 Classic. What convinced me to buy this tool is trying to adjust these jets with a screwdriver (well, I am kinda ham-fisted). Anyway, the SkewDriver fit these screws perfectly and I was able to back 'em out exactly 3.5 turns per FAQ recommendation (in fact I turned the left one out 3.5 and the right one just 3 turns). The bike now idles perfectly and pulls much better at low rpms (<4k) and I'm a happy camper. Bob#550 (Olympia WA).
• I am also sending a picture of my Carb Tools. Last year there was talk of using a Bobby Pin to adjust the carbs. Just snip it off and start adjusting. It fits easily into the tool kit. Also is a picture of a "store-bought" carb tool. This actually works the best of anything I have used. The rubber knob makes it very easy to do the adjusting. It is called Keihin FCR Carb Wrench Kit, MP# 08-0181 and is sold by Motion Pro Quality Tools & Controls. I found it at a non-BMW dealership.
  

Thanks to Andrew #870 for the piccie of the location.