idling at too high rpm

[plexiform]

I have an 88 R100rs that starts easily with some choke, idles fine around 1000-1200rpm at first. After riding a bit, it starts to idle higher around 2000rpm when in neutral at red lights. If anyone knows what could be causing this I'd appreciate some advice. I have tried unscrewing the screws on the carburater a half and even a full turn which makes it idle too low initially and then back up too high after riding a few miles. Thanks in advance.

88 R100rs
03 Guzzi LeMans

[20774]

Most likely a sticking advance. I think a way to test this is to put the front tire up against a wall and slowly let out the clutch in order to drag the engine RPM down. If the idle stays down at that point, then it's the advance. I've heard people getting some lubricant up into the advance canister to help lube things...there are people who can service the units as well.

You could also have some air leaks around the carb or between the carb and the head. Use some brake cleaner and spray around all the connections and the carb. If the RPM varies some when you spray the cleaner, then try tightening things up. It might be that the threaded intake stub that goes into the head has come loose. Most will remove the stub, clean the threads and use a high-temp thread locker and reinsert.

If you've been messing with the carb settings, you'll need to fix the problem with the idle and then go back redo you carb synch again...

Kurt in S.A.

[Motor31]

My vote would be for a sticking carb slider or cable. If it's been a while since they were synched I think it might be a good idea to clean them out and redo the synch.

[GlobalRider]

Most likely a sticking advance.

+1...or weak springs.

I used to just let the clutch drag with the front brake on and the RPM would drop to normal.

[jmerlino]

Another possibility (and please DAMHIK): If the carbs were rebult at any point and the butterflys were dissaembled, it may be that the butterflys were retightened on the shaft before the shaft's collar was tightened. If this happens, the butterflies can bind against the side of the carb and stick, and this effect can be more pronounced after they've warmed up a bit. The cure for this is to loosen the collar and the buttefly, retighten the collar, then retighten the butterfly. (Depending on how well the butterfly screws were staked, this can be really easy, or a bit PITA).

[lkchris]

Always adjust carbs--including cables--when engine is hot.

Fast idle very often occurs when carbs are adjusted cold.

[YoeFriday]

I have an 88 R100rs that starts easily with some choke, idles fine around 1000-1200rpm at first. After riding a bit, it starts to idle higher around 2000rpm when in neutral at red lights. If anyone knows what could be causing this I'd appreciate some advice. I have tried unscrewing the screws on the carburater a half and even a full turn which makes it idle too low initially and then back up too high after riding a few miles. Thanks in advance.

88 R100rs
03 Guzzi LeMans
Your bike is probably sucking air through the intake nipples. Pull you carbs off and see if they are still tight in the heads. If not, you need to let the bike idle in the shop til' it's starting to get hot.
Quickly remove the carbs again, unscrew the nipples and drop them into a cup of ice water for a couple of seconds. yank em out, dry them off, put on some quality tread lock and screw them back in. Once everything is back to normal temp, you should not beable to get them back out.
Put it all back together, re-balance the carbs and you should be good to go.

[PGlaves]

Both likely causes have already been mentioned.

Sticking advance and induction air leak. How to tell them apart.

If the high idle pulls down when you load the engine and stays down then it is most likely the advance weights sticking.

If the high idle pulls down when loaded but goes right back up without adding throttle it is almost certainly an air leak.

But, very weak advance springs could also cause it to go back up - but this is pretty rare. Usually even weak springs will keep the weights in close at idle RPM.

[lkchris]

Here's another cause of high idle, as strange as it sounds.

If ONE cylinder has very low compression, bike will experience runaway idle.