If you feel your carb issues are under control, here are a few more suggestions. First, the G-62 likes to turn up (higher RPM) and is very sensitive to prop loads. Loaded a bit to heavy and the RPMs will fall way down making one thing the engine has a problem. Your 22-10 should be about right but if it is a high load prop, that could still be a problem. Most anything 23" or 24" will be too large for the 62 though I'm sure there are exceptions. For a G-62 to be really happy, it needs to be turning from about 6500 RPM and up.

The G-62 is also very sensitive to mufflers and yes, yours may be too restrictive though I'm not at all familiar with your muffler. If you can get your hands on something else to try, that might be a good route to take.

You mentioned ignition modules so has this engine been converted to electronic ignition? If so, how is it timed? If timed with too little advance, your performance would be down.

Last and probably a question I should have asked first, is the engine in good mechanical condition? Does it have good compression when cranked? Does it turn freely? If these engines have ground contact with the prop, the crankshaft can twist fairly easy and an engine with twisted crank won't turn up as expected. You would also notice some runout at the prop tips and the engine would vibrate more than normal.

I hope some of this helped. These are darn good engines though they're not torquers like some of the rear intake, reed valve engines.