You do maintenance like changing gas filter, air filter, plug?

Take the muffler off and check for buildup.

give a dose of Seafoam and run it for a little while. Use new 89 octane gas and put Stabil in.

After all that, then worry about adjusting.

Clearing the muffler of carbon might help, but symptoms indicate your are running lean. Long term fix is to disassemble and clean carburetor. Seafoam or similar cleaner might help, but unlikely. If you are not getting enough gas flowing through jet to run properly, neither is Seafoam likely to remove built up varnish. As last ditch, open (turn left) the main jet 1/4 turn. Main jet is one closest to air cleaner. Jet closest to engine is idle circuit. This is same for both Zama and Walbro carburetors.

I opening main jet helps, now add Seafoam to gas and it should gradually clean things, to the point where you will eventually have to lean out (turn right) the main jet. If it doesn't help. You are going to have to get into the carb.