1975 R90 Idle Speed

[bbelk]

I have the idle set about as low (900RPM) as I can without having to rev it up some before take off. However, after the bike gets warmed up, it often fails to return to a low idle.

I can bring it down with the kill switch, or sliding the clutch a little and it will stay down once it gets there.

I have an Omega ignition system, so I don't think my spark advance is stuck, but I haven't checked.

What else will cause them to have two stable idle points. One at about 900 and one at about 2,000.

[Duane Ausherman]

You have classic symptoms for weak advance springs. Replace them. You can read up on this by simply using Google. Put in "bmw motorcycle high idle" and you will get a few sites. One of which is mine and it goes into more detail.

[bbelk]

Duane, are you talking about the spark advance return springs or the butterfly return springs on the carb.

I have a magic Omega ignition, so I don't have the spark advance springs, which is what I thought the classic problem was.

[Major Softie]

Yes, he meant the spark advance springs, so, it would appear that your "classic" symptoms are actually pointing to something less classic.

I would try running it on one cylinder and see if you can find the problem exists on only one side. If it does, it's the carb on that side. If it doesn't, then it's still almost certain to be spark.

[George Ryals]

Tune the idle after a complete warm up (25-30 miles) and everything will be alright. It'll take a little longer to warm up and idle without a little throttle, but you won't be revving at the stop sign.

[bbelk]

I would try running it on one cylinder and see if you can find the problem exists on only one side. If it does, it's the carb on that side. If it doesn't, then it's still almost certain to be spark.

On one cylinder I don't have a fast idle problem.

Tune the idle after a complete warm up (25-30 miles) and everything will be alright. It'll take a little longer to warm up and idle without a little throttle, but you won't be revving at the stop sign.

Warm idle setting has been my practice. When it is all warmed up, it has a TWO stable idle points. When doing the tuning, I seem to only be impacting the lower of the two. If I make the motor slow down using the clutch or the kill switch, it slows down and stays slowed down. If I reduce the idle, the low idle is too low (below 900 RPM), but hope springs eternal, so I will try again.

[Seth]

I've found on my Mystic that when the carbs aren't in sync, I get the same symptom.

[George Ryals]

My next guess is that it is too lean. Either from too lean mixture setting or air leak(s) between the carb and engine.

[Ken in Oklahoma]

I'm wondering Brad, how hard it would be to hook up your original points system instead of the Omega. That would sure tell you whether the Omega is a prime suspect or not.

The dual "stable" idle speeds baffle me.



Ken

[bbelk]

I'm wondering Brad, how hard it would be to hook up your original points system instead of the Omega. That would sure tell you whether the Omega is a prime suspect or not.

The dual "stable" idle speeds baffle me.



Ken

the original points are in there, but I have not touched them in over a year. I don't know if they would work, but I might try it.

The dual stable just means that it will idle slow and stay there if it is already running slow. If its running fast, it won't slow down until I do something to slow it down like fingering the kill switch or slipping the clutch.

I am going to miss you guys next week.