[Superman]

Stihl MS-180C. Starts fine. Runs fine for a bit. Then, it starts to act strangely. It will go into a mode where it runs fine at idle and half-throttle, but bogs down if you give it more than half-throttle. Then, it might return to completely normal. Other times, it will idle way too high and not bog down at full throttle. Then, it might return to completely normal again. I've cleaned (and removed, actually) the spark arrester screen, the air cleaner is clean and I've replaced the fuel pickup (fuel filter) twice.

I'm tempted to get the manual and start a dissection of the fuel system. The carburetor does not have an adjustable mixture. Only the idle speed can be adjusted. I wonder if there might be a pinhole in the fuel line, or something wrong with the fuel pump/diaphragm system. I know nothing about the diaphragm/fuel pump thingie.