Check the valve clearance for proper specs. That has been my experience with some 4 cycle engines exhaust valve stretched or burned. It could be a bad exhaust valve causing a loss of combustion gases. loger

It's running too lean.

Have him check his spark plugs (white or light tan colouration) one or both cylinders are running overly Hot . I concur with Bill that probably a lean condition is basic cause. He may have a gasket problem on the intake system .

I have seen a cherry red exhaust manifold on a 4 cyl fuel injection Volvo system due to a lean mixture after replacing an engine and the mixture h/n been adjusted. Otherwise, I have see it on small 4 cyl engines related to bad valves or valve adjustments. Good Luck! loger

Thanks for all the good infor. I've passed it along.

The good news is he has it working and it has gone back to the WalMart Super Center who owns it. The manager is very unhappy to pay him the $65 an hour, but his automotive folks can't fix it.....:-)

It all came down to valve adjustment. I'll quote from his email:

Conflicting opinions from two propane manufacturers, 5 and 7 thousandths from Onyx and 9-10 on both valves with aztec. Went back to 5-7 on the wet side (one piston had an oily residue) the other side was left at 9 and I'm not touching it!!! It's now running fine, no more cherry muffler. Wallyworld was also told they can call someone else next time unless my company takes over the routine maintenance. FAT CHANCE. The whole thing makes no sense to me!!!

Thanks for all the information. Just wanted to tell you how the story ended.

Ev