Small Engines (Lawn Mowers, etc.): 21hp Vanguard, air mixture, air filter

Question
My 21 HP vanguard, starts running poorly after warming up. It backfires sometimes, not much power under load. Fouls spark plugs where they are black in no time. only 225 hours.

Thanks for the help

Answer
Have you cleaned the air filter or carburetor?  A black spark plug indicates a rich, too much fuel or not enough air, mixture.  The carb is not adjustable but they are very sensitive to dirt/debris.

I would check the air filter and if it is clean I would start by removing, dis-assembling and cleaning the carb by blowing compressed air from an air compressor though all the carburetor holes/orfices.

Let me know if the air filter is dirty.

Eric