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Old 10-08-2012, 09:29 PM   #10
Unsprung Weight
JAB's Avatar
Joined: Dec 2004
Location: Beautiful Monrovia
Oddometer: 1,288
Originally Posted by KayAitch View Post
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.

OK, so you need to fix or replace the cap.

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

An air leak on a 2 stroke will make a lean condition that could cause a seizure. If the seal on the clutch side leaks you will suck oil out of your transmission.

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?

Maybe not so much at the carb and mount, but check that, but the rotary valve may have seals that leak. I don't know if that would allow air or oil or what to leak past.

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

When in doubt, gas it.

One more thing to check. Pull the baffle out of the muffler and make sure the openings are clear. If it is clogged, may cause it to run crappy in the higher RPM's.

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

Me too.

Thanks again.
1991 Honda XR628R
1978 Yamaha XT500
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