My engine was starting to lose some power too lately so I took off the muffler and was about to do that Dax modification with a hacksaw but I couldn't get the cap off. So I let things go but I did notice a buildup of carbon on the muffler pipe that goes in the cylinder. So I scraped it off and tightened it back down. Then i proceeded to check all the other nuts. The head bolts was a little loose about 1/8 of a turn it tightened down without I would say maybe 60 poot pounds of torque according to my mental torque gauge in my brain and the intake nuts needed about a half a turn. Then I took it around the block and my power came back.
Maybe this winter I'll change out all the gaskets,clean it up some,and try to figure out how to take that muffler cap off.