Replace the coil

From my experiences,
check for any cooling issues that would cause the engine to run hot first.

1. The spark
arrester (screen) on the muffler is usually my 1st check. Carbon blocking it reduces power and causes
heat to not exhaust. If carbon is on it, rem and heat red, with a
small flame (Lighter) then wire brush clean.

2. Look close to know rodents
have not restricted any air flow.

3. How old is the Eng?
Has it been serviced with good plugs and air filters for years?

Good Luck! Please Share what you find (Pics/Text or Both).