1971 BMW R75/5 idle baseline setting?

[krisnys]

Hi!

I'm trying to get my airhead to idle and run properly, and was wondering if anyone had tips on how to find a good starting point/baseline for the idle adjustment. I've read that the idle mixture regulating screws baseline is something like all the way in and then 1 + 1/8 turn back out again, but i haven't found any baseline adjustment for the butterfly stop screw..?

 

[20774]

What are the numbers on the side of the carbs? Probably 64/32/1 and -2 or 64/32/3 and -4 or maybe -9/-10. For the -1/-2/-3/-4, the idle mixture setting is 1.5 turns out according to the Bing manual. For the -9/-10, it's 0.75. For the idle stop screw, find where the screw mounts and watch when the screw contacts the arm. When it just makes contact, then turn the screw in one more turn.

 

[DonTom]

Hi!

I'm trying to get my airhead to idle and run properly, and was wondering if anyone had tips on how to find a good starting point/baseline for the idle adjustment.

If you have the stock Bing carbs on that thing, I doubt it's possible to get them to run properly. They are usually okay when cold, but will not idle when hot or even warm from the engine heat. And there are no decent fixes other than replacing those junky carbs.

I put Mikuni carbs on my 1971 BMW R75/5 many years ago. Main jet needs to be changed every few thousand feet of elevation change, but they are very easy to change at a fuel stop or whatever. Only takes a minute per carb. And my idle is now rock stable at any temp.

IMO, the stock 1971 Bing carb is the junkiest carb ever made for any vehicle.

-Don- Auburn, CA

 

[lmo1131]

The Bings on my '73 /5 ( 64/32/9 & 64/32/10 ) have worked fine from day one; they are a completely "new" design than the previous 64/32/3 & /4 used on the "early" /5s. The first series /5 carburetors are NOTORIOUS for poor idle, sluggish throttle response, surging in the mid-range, etc., etc.

To expound on Kurt's input,

Throttle baseline: you want the throttle butterflies to be open equal amounts. If the carburetors are on the bench this is easy to do. If they're on the bike; make sure there is slack in the throttle cables. Use a very thin piece of paper as a feeler gauge between the throttle stop screw and the arm ( I've been told ZigtZag is the thinnest ) and adjust the stop screw until it just grabs the paper as you pull on it. The idea being that you want the throttle stop screw to just kiss the arm. 0.00" clearance being the ideal. After that 1/2 - 1 turns IN on the throttle stops should be enough to get running. YMMV.

Bings are cranky; the idle mixture adjustment interacts with the throttle adjustment; change one and the other needs to be adjusted, back and forth until you get where you want to be. On the Keihins ( I have a Ural ) you set idle, then you set throttle at higher RPM. Done.

Before doing any of this, with the engine cold, make sure valve clearances are correct, and check your timing. Make sure no air leaks. Check vacuum port plugs (if you have them) are tight. And remember that carburetor ALL ( not just sync) idle adjustments need to be made with the engine hot so go for a ride (and don't forget to take your little screw driver and a 10mm open end for the cable adjuster lock nut).

Read this > http://bmwmotorcycletech.info/earlybingR75CV.htm