Odd symptoms: runs only on the front cylinder

[kell]

If a panhead has spark and 95 psi compression in both cylinders, what could cause it to run only on the front cylinder?

[Cotten]

You mean besides an Evil Manifold Leak?

[DuoDave]

I have had this problem. Turned out that one of the pushrod lock nuts had loosened off and the pushrod adjuster had screwed itself in so the valve would not open. Haggis encountered the same thing recently. I've heard that a spark plug can test okay in the open, but when screwed back into the motor will fail under compression. I have not come across this, but worth trying a new plug if you have not already done so.

[kell]

I had to leave the bike in a small-town bike shop a day's ride away. That was a week ago, I called today and they said it's ready. Will post what I learn.

[Jonderson]

I have also had the pushrod locknut problem. Didn't think much of it, and thought it was a flukey thing. Perhaps I ought to rethink that now.

Cotton, have you seen a lot of this?

[Cotten]

Uh,...no.

Normally, the adjustors are a very dependable and stable design, unless abused.

I've seen bent rods, broken rods, lotsa knarfed lock nuts and threads from over-tightening, etc.,...but otherwise, the only times I have seen rods drastically go out of adjustment was when fresh motors would beat a valve into a poorly cut seat, thus tightening the rod to where a valve would hang open; the opposite of what has been described.

Unless a valve is sticking or something gets under the valve, it is hard to think of a way it would loosen.