1978 R80\7 Idle

[shakyone]

Each time I stop with a warmed up engine, the idle is at about 1300rpm. After sitting for 30 seconds or so, the idle drops to a normal 1000rpm's. Float adjustment?

Thanks!

Paul

[Kurt in S.A.]

Could be sticking advance...clean and regrease. Could be air leaks. Could by previous synch was not done on a warm engine.

Could be low flow from the petcocks. The gas height in the bowl drops, creating a lean situation...IIRC that would result in rising RPMs. Then after sitting, the fuel catches up and the bike idles down.

Do the easy stuff first.

Kurt in S.A.

[Ken in Oklahoma]

Each time I stop with a warmed up engine, the idle is at about 1300rpm. After sitting for 30 seconds or so, the idle drops to a normal 1000rpm's. Float adjustment?

This is a common problem with most of the twin shock non electronic ignition airheads. That would include your R80/7. The problem probably has to do with weak ignition advance weight springs or an idle speed that is too high for the springs. The problem often shows up when you've been riding a while and come to a stop, especially with the transmission slipped into neutral.

The scenario goes something like this. Upon start up the idle speed is lower than when the engine is warm. So initially the idle is fine. However, as the engine warms up a bit the engine will naturally idle at a higher rpm. This higher idle speed will cause the advance weights to move out a bit, which will advance the ignition timing, which will make the engine idle even faster.

There is a quick easy test to verify the problem. With the engine hot and the transmission in neutral, the engine is idling too fast. You now switch off the ignition, either with the key or the kill switch, and let the engine spool down a bit. Then before the engine quits rotating switch the ignition on. If the idle stays low, as it should, you have now identified the problem.

The problem can be addressed in a couple ways. The first would be to install newer ignition advance springs whick, being stronger, will retard the weights swinging out. If the idle is correct the idle will stay low as it should.

Another approach would be to set the idle speed to a slower RPM, say 100 rpm slower. This lower RPM keeps the advance weights in the right place and the engine doesn't speed up.

I've dealt with this issue on a couple of my bikes by simply dropping the idle a bit.

I suppose it goes without saying that to deal with the problem your carbs need to be in good tune and balanced, at least as pertains to idling.


Ken