1980 R100S Euro - High Idle

[hsfarber]

Hi all-

I recently inherited a 1980 R100S in Airline trim (not germaine to the question but cool) that was originally a euro bike privately imported to the U.S. from a cousin who can no longer ride.

The bike runs great with the exception of the idle being high when the bike is warm. I have:

• Checked for intake air leaks with starting fluid - none found
• Adjusted the valves - the exhaust valves were a little tight
• Checked the advance by pulling the motor down to low RPMs and it went right back up, good thing because the advance mechanism seems hard to find
• Checked the throttle cables - seem OK but will probably renew on general principles

I guess the next thing to do is to try and set the mixture but I can't find reasonable instructions for the actual Bing carbs that are on the bike. The adjustment screws do not look like what is in the picture in the Clymer manual I have. I can find the idle mixture screw but not the throttle stop screw. I also can't seem to find the port for attaching a vacuum meter (which I don't have). I guess 1979-80 were intermediate years between the early bikes and the electronic ignition bikes of 1981-on.

One last observation, the plugs are black but not fouled.

Any thoughts of where to find some instructions or other useful pointers?

Thanks

 

[20774]

Welcome to the Airhead-side of the forum! Sounds like you've checked all the usual suspects, so it does seem like you're in need of a carb synch. Be sure and get the engine warm before you begin the process. BTW...what are the carb numbers...that might be helpful to point out the various adjustment spots. The vacuum port typically either sticks out the side (does on my /7) or can be on the underside of the carb. The throttle stop screw is a fairly large knurled nut that is turned with a flat-blade screwdriver...usually accessed from the underside of the carb.

Here's a video by our own Matt Parkhouse on balancing carbs:

https://www.youtube.com/watch?v=5bmJ0iYBYgQ

Here's another by Chris Harris...you'll have to get past the f-bomb early but maybe he's got some good advice:

https://www.youtube.com/watch?v=a_HyX1qLPbQ

Here's a long video by Boxer2Valve, a trusted source on Airheads. It covers several issues, so you might need to jump to the sync part:

https://www.youtube.com/watch?v=8H7PV2_CN-o

 

[hsfarber]

@20774

Thanks for the links they were helpful, I have all the adjustments figured out. Now I just need to do it

I am reassessing my thoughts on the advance mechanism though. It may well be that.

Cheers

 

[stevenrankin]

advance

On your bike, the timing advance mechanism is enclosed in a "bean can, the precursor to the electronic ignition system BMW started installing in 81. These point system in a can don't have the older advance weight system in fact, I don't even see an advance system on the microfiche for this year bike.

For the most part, they are reliable with little problems due to advance sticking unless you have a lot of miles on the bike or it has been sitting a long time and there is rust.

It is possible the timing is off or, the points enclosed in the cam are out of adjustment which can affect timing and idle speed.

Just some thoughts, good luck, you sound like you are heading in the right direction. St.

 

[guenner]

Riding with enricher (choke) open/stuck once the motor has warmed up could cause higher idle RPMs.

/Guenther

 

[pglaves]

On your bike, the timing advance mechanism is enclosed in a "bean can, the precursor to the electronic ignition system BMW started installing in 81. These point system in a can don't have the older advance weight system in fact, I don't even see an advance system on the microfiche for this year bike.

For the most part, they are reliable with little problems due to advance sticking unless you have a lot of miles on the bike or it has been sitting a long time and there is rust.

It is possible the timing is off or, the points enclosed in the cam are out of adjustment which can affect timing and idle speed.

Just some thoughts, good luck, you sound like you are heading in the right direction. St.

I believe - but it has been 35 or so years - that the points in a can had a mechanical centrifugal advance mechanism inside at the base of the can. If I recall correctly it could be lubricated through that little oval opening in the side of the can.

 

[guenner]

Remove the lid at the end of the can by removing the two Philips screws. Spray some WD40 in with the motor running.

/Guenther