Excessive backfire on starting and stopping of engine . Model no 31c707 . Engine Briggs& Stratton

Question edited for full 'make model (what it is)'.
Question moved from Cars and Trucks.

Same engine

LT
Craftsman LT1500 Engine Specs
Briggs and Stratton Engine

Engine Model ..................... Briggs and Stratton 31C707
Engine Type ..................... 4-cycle single cylinder OHV vertical shaft air-cooled gasoline engine
Number of Cylinders ..................... 1
Displacement, cu.in (cc) ..................... 30.5 (500)
Cylinder Bore, in (mm) ..................... 3.56 (91.0)
Piston Stroke, in (mm) ..................... 3.06 (78.0)
https://www.google.com/search?q=craftsman+lt1500+engine

LTS
Craftsman LTS 1500 Engine

Engine Model .................. Briggs and Stratton 31C707
Engine Type .................. 4-cycle single cylinder OHV vertical shaft air-cooled gasoline engine
Number of Cylinders .................. 1
Displacement, cu.in (cc) .................. 30.5 (500)
Cylinder Bore, in (mm) .................. 3.56 (91.0)
Piston Stroke, in (mm) .................. 3.06 (78.0)

https://www.google.com/search?q=craftsman+LTS1500+engine

..

Exhaust valve is not closing completely or the valve seat is cracked.

looks the rings are stuck.when you have head off check piston. john.

check intake valves for proper seating. If the valves do not close completely it will allow the engine to backfire thru the carb. Another possibility is internal timing caused by the misalignment of the timing gears between the crankshaft and cam gears.

I SET THE INTAKE VALVE AT .005 AND THE EXHAUST VALVE AT .003 AND THE EXHAUST VALVE MOVES ONLY HALF THE DISTANCE OF THE INTAKE. IT IDLES OK BUT GIVE IT SOME GAS AND IT BACKFIRES THROUGH THE CARBURATER AND SHUTS DOWN.

if you dont know take it to a proffessional if you make the slightest mistake you can bend valves or even worse break a piston

timing key under flywheel costs 1 dollar

Try posting this question under mowers. This is the measurement tools category.

Its your key under flywheel, its sheared or partly sheared. it doesn`t take much to get timming off.

Check you float in the carb I had one a few years back and it was partualy plugged cleaned it out and everthing worked fine. Also is the PTO binding up or bearings going bad putting an excessive load on the motor.