R75/5 High idling issue after carb rebuild

Hi everyone, as the title says, I rebuilt my carbs with new floats, valves, rubber bits and pieces, because they leaked on both sides and the bike was running rough in mid range. Those problems are gone now, but I have an issue with high idling I can't seem to resolve. When warmed up the lowest idle I can get is around 2,000 rpm. Here is what I have done:

-Made sure the cables are not sticking and there is sufficient play
-Completely turned out the idle adjustment screw, it does not even touch the tab of the butterfly valve
-Sprayed starting fluid around the carb intakes with the bike running to check for air leaks, no change in idle observed

What else should I check? Could it be that the butterflies are not installed correctly so they never completely close? I doubt it, but at this point I am looking at everything. I also just ordered the slider springs that are included from the /6 or /7 model on.

Appreciate any input, thanks!

Well, certainly the butterflies need to be in properly. Snowbum has a section on the butterflies at the bottom of this page:

https://bmwmotorcycletech.info/bingcv.htm

But it sounds like you need to go back to square one with all of the carb settings - idle stop screw, mixture screw - then get the bike fully warm. Place some fans in front of the engine and proceed with a carb synch.

- set idle mixture so that the cylinder runs at peak idle RPM, then richen it by about 1/8th turn...the idle mixture controls the flow of gas, so rich is turning the screw counter clockwise
- set the idle speed to match left versus right. You will need to have a way to short out a cylinder to see what RPM the other runs at, then compare and make adjustments
- set the throttle cable tension. Start with about 1mm of slack in the cable, and run the RPM up to about 1500 or 2000...lock it there. Then go back to shorting out each side and see what RPM the running cylinder settles in at. If you have one cylinder that is faster than the other, adjust the throttle cable to add slack. Recheck with the shorting approach.

Thanks for your input 20774. I am pretty sure I put in the butterflies correctly, but I will double check.
I had been thinking about making (or buying) the short-out tool, so maybe now is the time!

I'll report back how it goes.

Resolved the issue! I made myself two "shortening tools" and when I shorted out the left cylinder nothing really changed, idle stayed at 1,800, however shorting out the right cylinder immediately shut off the engine. So all pointed to the butterfly on the right carb. Upon further inspection, there was a gap between the butterfly and the casing that looked larger than it should be and after adjusting it, all works fine.

I still need to go through a good sync process, but since I now have the shortening tools and the Twinmax, that will hopefully be fun and go well!

Thanks again for the help, I didn't think the shortening would work so well! Olaf.

Thanks

Hey Olaf I didn't say anything in regard to your post as Kurt had the best advice.

I do want to say thank you for taking a few minutes to let all of us know what you found and how you solved the problem. St.

I feel like I "owe" it to give a reply, if someone is taking the time to give advice they deserve the "reward" of knowing if their suggestions work