Running without the muffler & not running with the muffler is either a blocked muffler or bad compression.
So now you take it off and have a good look at the rings & the bore,
Getting accurate compression readings is not particuarly easy with a 40 cube engine let alone a teaspoon.
Then there is compression both above & under the piston and the latter is far more important than the former.
You would not believe how many times I get a hand held in for service tha has just been loaned to son / daugher/ neighbour to find it is totally stuffed.