Mikuni Trouble?

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Jul 10, 2008
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I have checked the troubleshooting guide on this, but no go.....

Was out riding yesterday and the bike performed flawlessly for 75-80 miles. Coming back into town, the bike lost power and died. I checked the gas and saw it was fairly low, but still had some in there. I kicked the bike over and wouldn't restart. Even though the engine was warm, I choked it (or actually engaged the starter plunger, it's a VM34) and was able to get it to run after the 2nd kick, but it was revving to about 4000 rpms. Once I disengaged the choke, it would die.

I also noticed that if I started it and disengaged the choke and gave it about 3/4 throttle it would try to stay running. I was thinking that the pilot jet was clogged and so the main jet was doing the work, and that's why it wouldn't idle, either.

So I got the bike home and took apart the carb, which is brand-new. Sure enough, the pilot jet looked fairly clogged, so i boiled it and the main jet in some lemon juice and water, cleaned out the rest of the carb, and tried it again.......and the same thing happened. The bike starts and the engine immediately revs like crazy with the choke on and dies with it off.
So what's up with that?

Another Question:

This bike had some rust in the tank and the jets fouled once before. The carb and the tank were cleaned and dried out. There might still be some residual in the tank though, and I thought that maybe the carb was sucking some of that in once the tank got low. A guy that worked on my bike said that in the past he had coated tanks with a product they use to rust-proof radiators. It was called red-something-or-other. He said it was extremely durable and better than most other tank coating products, without the risk of a coating that doesn't completely dry and then fouls the whole fuel line . Has anyone else ever heard of that?
I think many of us have favorite tank coatings. My current favorite is KBS coatings, but I just bought another kit from Eastwood because it was on sale. I've used thiers before with good results.
I'm sure you will get some opinions here, the one I've heard bad things about is Kreme, if I have spelled that right. Some folks say if improperly applied it flakes.
My 64 Norton needs sealing this winter for the rust flake prblem and it is a good rainy weekend project. If your paint is good wrap the tank with plastic before starting.
Follow the driections with the kit very carefully and don't take any shortcuts. They often have you apply two types of acid so handle and dispose of carefully.
Do as you oughta add acid to wata.
Well, I have a theory about this. I'm thinking I have a vaccuum leak. When the enricher plunger is used, the gas mixture is overly rich and it uses the added air to immediately run the engine up like a wild man. When the plunger is disengaged, the pilot jet is used and the mixture is then too lean to combust with the added air. That would also help explain the reason why the engine would try to fire when the throttle was cracked way open. Does that make sense?

I suppose my next step is to try a new gasket between the bowl and the body. Does anyone have any advice about properly sealing everything up? Could there be any other place, other than at the manifold, which I checked, that it could be leaking air?

Don't worry about the gasket between the bowl and the carb body as long as it is not leaking gasoline. The float chamber IS and HAS TO BE vented to the atmosphere, say, you haven't somehow closed up your bowl vents. If you have that can cause the strangest running problems, I have seen the time those little mud wasps had filled the end of a guys vent hose with mud, he was tearing his hair out before he found the problem. Check for air leak by spraying carb clean on the manifold joints while running the engine, good luck.
Yep George,

My Mikunis work fine with it vented the way you reccomended.
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