5521 bbc mower backfired then stopped only backfires when i try to start

Change sparkplug. it should be ok

Carburetor needs adjusted. May need rebuilt or just cleaned. Could be one of the jets is plugged.

Does it start but backfires when running? Or does it just fire/backfire when trying to start? First thing I would check is the flywheel crank key isn't sheared. If the key us ok then check valve clearances

sounds like the carb needs to be rebuilt

first smell the oil is there a gas smell to it?the needle valve maybe dripping fuel and over flowing into the intake

It can't be tuned to stop it backfiring. You need to let it idle for a minute before turning it off. This will stop it backfiring. Regards Phil

loose piston wrist pin will seize an engine eventually

my 15 hp kohler engine backfired while i was using it, now it wont crank and backfires thru carb

backfire will be normal if shuting engine off at full throttle. Idle engine down as low as it will go before shuting off and that should stop the backfire. Look under motor at pulley area and make sure there are no oil leaks, if not you have an internal engine problem rings or valve seals.

Did you hit something? Sounds to me like a flywheel key sheared off or a major internal part broke. My thoughts are you will need to take this to a repair shop or individual that can comfortably tear into the engine.