Idle hands, devil's work

[keelerb]

I can't seem to get the idle on my 84 R100RT right. When I adjust and sync, I set at about 1100 RPMs. DId this today. Tonight I took the bike out and the idle was below 800, to the point where the bike won't stay running without a hand on the throttle. This was true even after 20 or so miles, so motor was at operating temperature.

Only thing I can think of is when adjusting it the engine may be getting really hot (I usually try to put a fan on it, but with the fairing and all I'm not sure that does much. Today I was pretty quick about it so I didn't even bother with the fan.) Maybe the idle at "superhot" temps is equivalent to a much lower idle level at normal operating temps?

I'm open to suggestion! :banghead

[mneblett]

Are you doing a 10-20 min. ride *before* doing the idle adustment? That not only gets the engine up to temp, the air flow back over the Bings gets them up to temp as well. Once the entire engine/carb package is at operating temp, then you can pull up in front of the fan, hop off and do the idle and snyc adjustments.

[keelerb]

Oh yes, the motor was well warmed up beforehand. I went out for a ride and was experiencing excessive vibration so I headed home to do the sync. Was out for at least a half hour or so before the idle-setting/sync'ing exercise.

[James.A]

The two things that affect idle stability in my experience are valve adjustment or intake vacuum leaks. Particularly, when I was battling exhaust valve seat recession on my 750, the thing would not idle at all after achieving operating temperature if the exhaust valves had tightened up. In the last few hundred miles before I took the bike out of service, a single hard run of 50 miles would croak the valve adjustment and cause the motor to not idle. Your 1984 R100 is a model know to be succeptible to this phenomenon. (or a similar affliction, valve plastic deformation)

A properly functioning airhead should need a dose of enrichment (choke) on cold starting (ambient air temp under 80F +or-) and then should idle normally in any circumstance once the temperature in the combustion chamber comes up and enrichment is closed off.

[amiles]

If the previous good advice fails to help, I would suggest that you read page 14 in the "Bing Carburettors" book, " Trouble Shooting Idle Circuit Problems".

I was having similar troubles and the directions in the book helped me to get things right. If you don't have the book it is reasonably priced and will be of great value to you.

[orbitangel]

I can't seem to get the idle on my 84 R100RT right. When I adjust and sync, I set at about 1100 RPMs. DId this today. Tonight I took the bike out and the idle was below 800, to the point where the bike won't stay running without a hand on the throttle. This was true even after 20 or so miles, so motor was at operating temperature.

Only thing I can think of is when adjusting it the engine may be getting really hot (I usually try to put a fan on it, but with the fairing and all I'm not sure that does much. Today I was pretty quick about it so I didn't even bother with the fan.) Maybe the idle at "superhot" temps is equivalent to a much lower idle level at normal operating temps?

I'm open to suggestion! :banghead

OK, KB, here are a couple of suggestions:

1. Have you verified that your static ignition timing is correct, i.e. plugs fire at the "S" mark and not any later? Retarded ignition timing will cause a slow idle RPM.

2. Have you checked your compression? You might have low compression.

FYI, I recently had a situation where my RS would not run at all without the help of the starter motor. Timing checked spot-on. Nice fat sparks from the plugs.

Turned out that my 5 month old, $17.00 BMW (gold cadmium plate) condenser was defective. If you have one like that in your engine it also might have failed.

Motorrad Elektrik says these (recent Bosch) things are JUNK! Believe it. In thirty years I have NEVER had a condenser fail - until this "new" one did.

Hang in!

Charlie

[keelerb]

Thanks folks. Believe me, the bike is otherwise in tune and good shape. I do all my own maintenance and I'm completely anal, excuse me, punctilious about this. Valves haven't moved during my ownership (which is only ~6K miles), timing is good, compression is good and equal in both cylinders. And the bike runs like a top!

I will experiment a bit more. I do think that this is temperature related, but WTF knows? :scratch