There's always the option of buying a new muffler I guess. A little over 20 dollars on ebay..I'm not even sure if it's carboned up at this point, just the only thing I could think of keeping the saw from running.
When the saw has 150 compression and ignition and you squirt fuel into the cylinder and it still doesn't run that's all I could think is left. Fuel is good, tried it in a different saw. I'm not sure if you can run these saws with the muffler off to test or not. I'm soaking it in Simple Green for a couple of days.