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Old 10-08-2012, 07:18 PM   #9
KayAitch OP
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Joined: Sep 2012
Oddometer: 95
I believe this to be the case. Pre top-end rebuild I would ride along and release the cap every 5 minutes or so because I was aware of this venting issue (I have pulled the hose off the tap previously after it has cut out to find no fuel coming out of the tap. Also, emptying the tank I would get a little run out of the tap but then it would stop. Releasing the fuel cap would start the flow again).

During the running in I wasn't bothering to open the fuel cap because I thought the vents were clear.

What does a leaky crankcase do that would cause this? Again, apologies. I'm learning as we go :).

Yes it is a rotary valve with the carb inside the engine case. I have heard of leaks between the carb and the mount before. Again, would this cause this cutting out condition?

The loading up does clean up after a couple of accelerations, thanks.

I really hope I don't need to split the case.

Thanks again.

Originally Posted by JAB View Post
Sounds like you have the venting issue on the run. As far as the seals are concerned, due to age the seals may be hard and leaking air. Is this a rotary valve engine with the carb inside the engine case? If so, that may be another place for an air leak. The crankcase sealing can be leak-down tested, but I have no way to tell you the right way to do that. To change the seals (if they are even leaking) you have to split the cases. The loading up issue should pretty much clean out once up to operating temp. It may come back a bit if the engine is "lugged" at low RPM but should clean out again with a twist of the wrist. Gotta love the little old 2 smokes.
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