Please help I have a Craftsman 15.5 hp with a Briggs&Stratton 2N8707-0173 engine. Engine usually backfires when stopping, but now refuses to start. It does not even try it just spins. I have: Checked Oil, fuel. Removed flywheel bolt and checked the key. Removed and cleaned the carb. Checked the solinoid at the base of the carb is retracting when the ignition is turned on. Checked the spark by holding the sparkpulg against the engine. It was weak so replaced the coil and now is very bright. Checked the valve clearences, the inlet valve had a gap of approx 1/4 inch, not sure how it was running but the end cap was still in place so adjusted it by eye to approx 1mm. In desperation tried pouring gas in the carb while cranking the engine but nothing. Finally tried spraying easy start which resulted in the engine backfiring twice. I don't have a way to test compression but it was running fine prior to stopping. Any ideas?