High Idle on '83 R65

About 4 years ago, I bought a 1983 R65. When hot, I would pull in the clutch and the engine would want to idle at 2500-3000 rpm. If stopped, I could put it in gear and start to let the clutch out; once the rpm dropped under 2,000, the engine would settle down to an idle of 750-800 rpm.

I posted those symptoms here and a few folks said I had a bad Hall Effect sensor. I removed and dismantled the bean can, cleaned and lubed the flyweights, and re-assembled the can. When re-installed, the idle issue was mostly gone, and when blipping the throttle, I could feel the famous BMW torque. The idle issue returned about 150 miles later.

So, in November of 2013, I bought a new Alpha 1 igniton kit (bean can, ignition module, Dyna Coil, wires, and plugs). Time flies; earlier this week I actually got the
Alpha installed. The spark timing is spot on (The first tab is centered in the hole at 800 rpm and the second is centered at 3,000 rpm).

I took it out for a run and it is much smoother than before. However... it was a 90 degree day and after 8-10 miles at 55-60 mph, I came to a soplight, closed the throttle, and pulled in the clutch; the engine continued to idle at 3,000 rpm! Again, if I slowed the engine by starting to let the clutch out, once the rpm dropped below 1,800 to 2,000, the engine dropped to a smooth 750-800 rpm.

Any and all ideas as to why the engine want to idle fast when hot, even with a totally new ignition system, will be greatly appreciated.

Thanks in advance,

Larry

Carburetors?

It sounds like you have the ignition side pretty well covered so you may find the cause of your problem in the fuel (carb) side. It could be an air (vacuum) leak somewhere or it could be stiff throttle cables that get stiffer with a little heat from the motor and ambient temp. Be patient, the guys that know much more than I do will chime in and give guidance with some very sound advice.

When were the carbs last synched? That should be done after a 20-30 minute ride.

When that happened to me, I think I found the problem in the float adjustment. Too much fuel in the bowl so some was getting into the enrich circuit on ine side.

Exactly the issue I had with my /5, until I synced the carburetors. Make sure your valves are correctly adjusted before you do this (done cold, before your twenty minute ride).

Had the same problem on my 1981 model.Turned out to be the intake sleeves between the carbs and the head, they get hard and allow excess air to be pulled in causing high idle. Replaced the rubber sleeves and it fixed the problem.

Easy enough to check for an air leak between the carburetor and the head with a spritz of any flammable propellant aerosol.; a quick shot, if RPM increases, it's sucking air. But given the length of time this has been going on, 4 years, a valve would more than likely have been toasted if it were sucking air.

My buck's on carb sync. Not hard at all to do, but a lot of folks ignore it.

Thanks folks!

I haven't synched the carbs in over a year; 'tis now on my to do list!

Thanks!

Sounds to me that the slider/piston in the carbs get hung up at a higher RPM. Could be just on one carb.

Just remove the elbow from a carb and push the piston up with your finger and check if there is a resistance.

I would disassemble and clean slider/piston and I would also check the diaphragms.

When this happens, can you check that both arms of the throttle's butterfly shaft have returned to their idle positions?

/Guenther

Had same symptom on an '84 R100RT.

The problem was low compression in one cylinder.