Higher RPM's

I have been reading the posts again and think I understand my problem but want to make sure.

The motorcycle is running wonderful; however, when it gets hot, the RPM's go up at idle They can go up 1000 to 4000 RPM's. When I turn the bike off and start it again, most of the time the RPM's go back down. I don't think it is the throttle sticking. I have tried to test that.

I have replaced the manifolds from carb to engine. I have cleaned the carburator. Really she is running nice.

From what I have read, it maybe that the mixture is wrong. Any ideas?

 

When the RPM's are at 1000 rpm's ...

Secure the Throttle Cable Sheath to the Frame Center Tube with a wrap of Duct Tape.

Eliminate the possibility that the Cable is being pulled-on a little bit.

 

Either you have a vacuum leak somewhere or you're not sync'ed.

Mixture tweaking is the final step.

 

Hmm.. I've had the same problem..

The bike is perfectly sync'ed using a YICS tool, there doesn't appear to be any issues with vacuum leak (I tried the propane test).. But looking at it with the colours with the colortune, I couldn't get the "Yellow" on some of the cylinders, no matter how much I twisted the mix screw.

Someone here (it may have ben you Fitz) suggested I squirt neat seafoam into the pilot air jet hole, this causes the passages going to the pilot jet to be cleaned, resulting in a clean pilot jet tube. The pilot jet is the only thing that supplies petrol to the engine at idle I think, so perhaps cleaning that will help??

I'll let you know when I've done it.

 

Good ideas everyone. I will go about my business and get some of this done.

Swissjon, let me know what you find out.

I still think its interesting that you turn it off and back on and everything is back to normal.

 

Some Members have done Compression Checks and found their Bike was not as healthy as could be.

You might be dealing with an issue such as that.

 

Fair enough, hadn't thought about the cylinder internals, could be worn rings I suppose. Any idea what a good reading should be? 130? 140? Higher? Lower? (LoL freeze!)

 

The actual numbers may vary ...

150 ~ 155 psi and up = Excellent

130 ~ 140 psi = Fair to Good

120 psi and below = Poor

 

For the record, I have NEVER recommended SeaFoam for anything except helping flush out a de-rusted gas tank. I quit using it as a seasonal fuel stabilizer because it adversely affected the bikes' performance.

Vacuum leaks can be sneaky. I just discovered that two of the vacuum port caps on my '81 were LOOSE, and DANCING AROUND on the spigots even though they looked fine. Hard as rocks, not plugging anything once they started their vibratory dance. I'm gonna post a thingie about them as soon as I get more pics illustrating how HARD they are. They're rubber and you can't squish them with pliers.

The other really insidous vacuum leak (ask MiCarl and Lt. Dave) can be throttle shaft seals that only leak when the throttle is opened past a certain point. You'll never find that with propane.

Honestly though, hanging idle almost always comes back to sync (or a REALLY out-of-whack float, or both.) And you can't begin to diagnose or fix unless you've torn the carbs down and cleaned them properly.

Perpetually lean isn't a symptom of low compression; but it does pay to run a compression test as part of the tuneup regimen, as called for in the book.

NO SHORTCUTS, REMEMBER? SeaFoam ain't the answer. Hard, tedious, patient work is. Clean your carbs right, set the floats right, bench sync, vac sync, THEN ColorTune.

Then you can ride the bejabbers out of it.

 

Lol. You can't get seafoam over here anyway, I just used ordinary carb cleaner. I tore the carbs down, cleaned the bit I missed last time and got the carbs on within 2 1/2 hours. A new record for me.
I'm not going to be able to ride it until after the weekend, but when I started her, she did sound a little happier. I don't want to ride the bejabbers out of her lol She gonna be my commuter bike, so long as I can stop pulling her apart long enough

 

Swissjon, You made the thread even better. Once again everyone was very helpful. Much more to learn to tune the carbs right. I know the whats. Now I need to know the how to's.