I don't have a torque wrench (should probably get one) but to me the bolts seemed a little loose (especially the two by the exhaust) so I tried tightening them up a bit but it didn't do anything.
I haven't been able to spend much time on this thing lately because it is only cool enough to work outside before 7 in the morning or after 8 in the evening. I still have to pull the carb off again and see if there is anything wrong (like the ball-check valve you mentioned) in the little yellow plastic fuel tubes.
Maybe one of these days the weather will be cooler and it will give me break so I can work on it. I would take it to the service center but since they are the only one around here they said they are 10 weeks out (
) on doing any repairs or service for anyone (I guess partly because they service chain saws for the forest service so they are probably very busy).
So, maybe one day I can tear into this thing myself. They aren't especially complicated are they? Where do you start (or what are the basic steps) and what do I need to look out for in the disassembly process? Also, what should I be looking for that might be a sign of the trouble (besides the head gasket)?
Last, I noticed that the top of the piston is very black and oily and nasty looking. Does that indicate anything?
Once again, thanks to everyone for the help!