Our Stihl leaf blower would start and idle, but would only spool up to about half speed. I figured it was a clogged spark arrester in the muffler. I wasn't looking forward to taking it apart, but a quick look revealed that the spark arrester can be removed without taking the muffler off.
The spark arrester unscrews right out of the muffler.
The screen was almost totally blocked.
Burning the carbon out with a MAPP gas torch.
Spark arrester is clean and the leaf blower runs like new.