OK, so I spent some time diagnosing the rough running on my 31 PA.? Pinned it down to #2 cylinder (no compression).? Confirmed by looking at the valvetrain (side cover off) that both valves are moving so neither is completely stuck.? Turned the engine until both valves were definitely closed and shot some air from my compressor into the spark plug hole.? It comes right out the carburetor with no resistance.
SO: my #2 intake valve is either stuck or otherwise malfunctioning.? I do know that all four cylinders had good compression last fall just before "something went bad", so this problem came on quickly.? I've run a heavy dose of Marvel Mystery oil to no effect.
I'm a decent backyard mechanic for small jobs but pulling the head and working on the valves -- with no shop manual and only primitive understanding of this engine design -- makes me nervous.? I plan to try and find a local mechanic who is willing and competent to open this motor up and resolve the problem.? If anyone happens to know a resource in the Portland Oregon area, please let me know.
Thanks!
Somebody in the Cascade Pacific Plymouth club will be sure to help. Contact president Don Hufschmid at 503 577 7899 In the meanwhile, a good soaking of your Marvel Mystery oil, or just plain diesel oil will likely unstick the valve. Burning outdated gasoline is a sure way to bring this problem on.