Small Engines (Lawn Mowers, etc.): briggs 20.5 hp, sympton, intake valve

Question
it pulses gas/air mix backwards out of carb while turning over with starter,just curious about possible causes in general for this sympton.ty very much for any assistance.

Answer
You need to clean the carb. The fuel coming out of the carb is caused by the piston coming up slightly before the intake valve closes. This engine usually has a "spit guard" that sits right in front of the carb opening, it keeps fuel from getting onto the air cleaner.
You normally don't see the "spit" unless your carb is leaking over.