Small Engines (Lawn Mowers, etc.): Craftsman Lawnmower Issues, craftsman riding lawnmower, speed jet

Question
My 19.5 hp B&S craftsman riding lawnmower has trouble starting/when running it "surges". The RPM's seem to vary up and down also when throddled down it dies. Anything to help-thanks  

Answer
Most of the time this is caused by a dirty carburetor.  Have you checked/replaced the air filter?

If the air filter is clean then I would suspect the main high speed jet in the carburetor.  

It is best to remove, dis-assemble and clean the carb with compressed air and carb cleaner but you may be able to remove the high speed jet bowl nut and just clean the jet.

Let me know if this helps.
Eric