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Discussion Starter · #1 ·
I recently finished rebuilding the carbs on my 1100 using Randakk's kit, the instructions in Howard Halasz's book, and a few odd parts and lots of help from the kind souls on this site.

I rode it for the first time two days ago, and when riding the bike at moderate speed, all of a sudden the rpm will shoot waaaay up, almost to redline -- and way above where the hand throttle is twisted. It's happened about five times now in 80 miles. It even happened while I was synchronizing the carbs.

What's going on here? Any ideas out there? Thanks.
 

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I had a SIMULAR problem with my old '76 wing. It actually was 2 problems. 1, was the gasket between the two plenum half's blew out, and was dumping gas into the motor. After getting a new one , the number 2 carb, was overflowing and flooding out the cylinder. Once I figured out what was happening all was good. Remove the air filter and look into the intake for gas sloshing around or bubbling up from the seam. Hope this helps.,,
 

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check your cable. make sure it operates freely and there are no sharp bends or twists. check cable adjustment, both at the handgrip and the one inline. if the cable is too tight it will cause high rpm.
 

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the engine cannot run that high without enough air. something has to be wrong in the throttle plate control
 

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when riding the bike at moderate speed, all of a sudden the rpm will shoot waaaay up, almost to redline -- and way above where the hand throttle is twisted.

It even happened while I was synchronizing the carbs.
You need to refine your story. At speed, and the rpm shot way up indicates a slipping clutch. Otherwise it would have accelerated.

At idle, the clutch is not part of the scenario. Unless you're "syncing while driving", and that's illegal in all states.

So which is it?
Check your throttle cable routing and rpm changes when turning.
 

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Discussion Starter · #7 ·
You need to refine your story. At speed, and the rpm shot way up indicates a slipping clutch. Otherwise it would have accelerated.
Sorry. I thought about that: I'm thinking that I must have squeezed the clutch immediately because I don't remember feeling a lurch forward when riding. And it definitely happened in neutral while I was adjusting the vacuum. When it happens again, I'll try to pay closer attention to my left hand. Maybe I have two problems?

FWIW, it hasn't happened since I did the synchronization, but I really doubt that that would affect it. And except for this problem, it does run better than it ever has with the rebuilt carbs and the sync now complete.

Oh, and I will check the cable routing and the rpm when turning. It did happen once when I was leaning left in a turn. (Unnerving, it was, too.)
 

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Discussion Starter · #8 ·
Vacuum leak? Maybe the hose for the advance, or a loose sync port screw?
Now that you mention it, one of the screws for manifold adapter wasn't tight. Could that have caused this?
 

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Discussion Starter · #9 ·
Update

Check your throttle cable routing and rpm changes when turning.
I didn't have a chance to ride it today, but I put it in neutral on the side stand and ran the engine up to 3000 rpm several times. Then I leaned it to the right as far as I could and did the same thing. Could not duplicate the runaway rpm that way. At least not in 20 minutes. Of course this doesn't quite duplicate turning while the bike is in motion, so I'll do that.

Also removed the air filter and looked into the plenum while it was running for about 20 minutes or so. No sign of any gasoline in there. I then removed the air box to check the throttle cables, and there are no kinks or sharp bends in them.

I think maybe the cables could be tighter in the bracket on the carburetor. Could this cause runaway rpm?
 

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I didn't have a chance to ride it today, but I put it in neutral on the side stand and ran the engine up to 3000 rpm several times. Then I leaned it to the right as far as I could and did the same thing. Could not duplicate the runaway rpm that way. At least not in 20 minutes. Of course this doesn't quite duplicate turning while the bike is in motion, so I'll do that.
I believe glhonda meant that you turn the bars lock to lock with the engine idling. If there's any change in rpm doing so you have a cable problem.
 

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Discussion Starter · #11 ·
I believe glhonda meant that you turn the bars lock to lock with the engine idling. If there's any change in rpm doing so you have a cable problem.
Thanks, Ken. I'll do that tomorrow.
 

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I believe glhonda meant that you turn the bars lock to lock with the engine idling. If there's any change in rpm doing so you have a cable problem.
I saw a BMW like that last year, owner was at Honda dealer thinking of trading it in.
He'd turn the bars most the way to the right and his engine would rev way high.

"I think maybe the cables could be tighter in the bracket on the carburetor. Could this cause runaway rpm?"
Sure could! Might be the problem.
If turning the bars pulls against the cable and it slips, then it's about the same as twisting the throttle more. Carbs don't care how they get pulled, they just open up when pulled on.
If you can reach in there give a little pull on the cable with your hand and see if it slides and pulls open the carbs.
 

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Discussion Starter · #13 ·
I saw a BMW like that last year, owner was at Honda dealer thinking of trading it in.
He'd turn the bars most the way to the right and his engine would rev way high.



Sure could! Might be the problem.
If turning the bars pulls against the cable and it slips, then it's about the same as twisting the throttle more. Carbs don't care how they get pulled, they just open up when pulled on.
If you can reach in there give a little pull on the cable with your hand and see if it slides and pulls open the carbs.
Thanks, Chromo, I'll try that.
 

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Discussion Starter · #14 ·
Update

I got a chance to ride today, so before I left I turned the handlebars from stop to stop at idle, and there was no change in rpm.

The throttle, however, is very stiff. In fact it's like a built-in throttle lock; it stays wherever you put it, so something is not right in the return linkage or cable. In fact, it seems stiff in both directions. The rpm didn't race way up for no apparent reason today, but I noticed that the throttle wasn't fully returned a couple times when I shifted, and it went up then, of course. Maybe that's part of it.

So the throttle does not return by itself -- has to be turned manually. I assume that means it's too tight. Correct? Thanks.
 

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The cables too tight will do that, or too tight a bend or a bad cable.
 

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Discussion Starter · #16 ·
The cables too tight will do that, or too tight a bend or a bad cable.
OK. Thanks, Dave.

Could I ask one other question: If I move the adjusting nut just under the right handlebar toward the hand-grip, am I tightening the cable? Thanks.
 

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screwing the cable adjusting nut in toward the handgrip would be loosening the cable. there should also be another adjuster under the false tank. screwing this inward or towards each other would be loosening the cable.
 

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Discussion Starter · #18 ·
screwing the cable adjusting nut in toward the handgrip would be loosening the cable. there should also be another adjuster under the false tank. screwing this inward or towards each other would be loosening the cable.
Thank you, trashtruck. I'll be working on that first chance I get tomorrow.
 

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I'm speaking from my experience with my 1200, should be the same.
The pull cable screws into the throttle housing and is held tight by the lock nut. There is no "adjustment" at the handle bars.
As stated before, the pull cable is adjusted by an adjuster under the faux tank. Notice what happens to the push cable freeplay as you adjust the pull cable. It will give you a better understanding of how they work "together".
 
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