KrazyKen,

There was another thread about two months ago, dealing with the MVVS .45, with the same #3245A muffler.
Similar observations.

This muffler is VERY quiet, I am told it is 4 db lower than the OS.46FX with the standard, baffle included muffler.
But it is also excessively restrictive.

On the other hand, the MVVS with the #3248 tuned silencer, may not be as audibly offensive as you think.
MVVS recommend adding a length of 1cm i/d silicone hose at the end of this tuned silencer, to reduce noise considerably.

Try to measure this engine with it. It is quieter than with the standard #3245 muffler.

Buying a used engine has its pitfalls. You can never be completely sure what you are getting. Try removing the glow plug and turning the engine over. You should feel a slight "pinch", as the piston goes over TDC.

If you feel nothing at all, you may have bought an engine that was either;
1. Broken in very rich, four-cycling (it should be done only two-cycle rich, as a tapered bore engine).
or,
2. Has accumulated over 150 running hours, or a large number of lean runs.

It does sound to me, more like a "constrictive" silencer problem.

This, although your compression tests make me think otherwise.