14.5 hp briggs & stratton backfire issue

S

steveandjere

Forum Newbie
Hey everyone

I have a Simplicity mower with a Briggs and Stratton engine Model 28770 after engine is warm 5-10 Minutes starts to backfire from both carb and muffler. I have replaced the Carb, spark plug, cleaned the flywheel, rechecked all my gaps. Any ideas. Mower had been sitting for 2 years
 
Hello.

Your backfiring could be be caused by poor quality fuel which would explain the backfire out of the carburettor.
Alternatively it could also be the engine running to lean on the carburettor which would also cause this to happen.
 
If it's been sitting for 2 years, you may have corrosion in the fuel solenoid. Remove the solenoid from the carburetor bowl and see if the plunger moves up and down. If it's stuck, clean it good with carb cleaner. Then test the solenoid by grounding it to the engine and touch the solenoid power wire to the positive battery terminal to make sure the plunger works. If it works, reinstall the solenoid and see if it still backfires. If the plunger doesn't move, you may have a bad solenoid.
 
If it turns out to not be a fuel problem you might look at the valves. A sticky valve can cause excessive back firing if not closing proper when the motor fires.
 
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