Rcimp,

That's an interesting theory about the exhaust valve. How true it is I have no idea. I don't think the intake valve would start to open until the piston was past TDC a few degrees. If the exhaust valve were set too loose, it would probably only be by a few thousandths at the most and it doesn't seem like, coupled with the fact the piston was now on a downward stroke, that there would be much 'backwash' into the intake and up into the carburetor....whew, what a long sentence!

But who knows, maybe so. I looked at some of your previous posts and there seems to be a string of problems and unanswered questions on your rig. Some heating issues and a few valve adjustment questions.

If all the tune-up parameters could be met, valves perfect, timing right on, carburetor tuned and functioning then there would be a benchmark to go from.

If the truck is in the shop right now, the mechanics are qualified (for a old bolt engine) and the hourly labor rate isn't astronomical, it might behoove you to have them figure out exactly what is wrong. Good luck