After far too many pulls on the recoil starter, it became apparent that this engine was suffering from more than just a simple malady. I pulled the head this afternoon, and found that the intake valve was frozen in its open position. Crazy! After liberal applications of WD-40 and plenty of tapping with a hammer, I was able to work it loose, remove and re-install it and the engine runs great now. It started on the first pull when I re-assembled it, so I suppose it's happy again. I'll change the oil to flush out all the solvents I've been using on it, and hopefully it'll be good from now on. I just don't understand how the valve became dry in the first place. There seems to be a provision for splash-lubrication, but who knows? The exhaust valve was perfect. At least I'll know what to do if this happens again.
Thanks to all who cared enough to comment. :smile: