Need a little small engine assitance, if possible...

Thirds on cleaning that spark arrester screen in the muffler, but I wouldn't toss it unless you're willing to pull the limiters on the carb screws and diddle the mixtures. The epa runs them wicked lean as is and the spark arrest screen creates enough back pressure when clean to keep them jetted properly.
The clogged screen default richens the mixture; a safe operating condition.

Tossing it risks leaning the motor out. Not good when it's a heat prone motor running wot most of the time.


Based on your description of the running condition, is very likely there's a very fine fuel screen just past the fuel inlet on the carb, and it's probably got a clearish layer of Schmootz on it. I would NOT disassemble the entire carb. Just pull the top plate to find that screen, blow the gunk off with carb cleaner, and reassemble.
don't lose the wee screen.