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The first 2 mowings of the year the tractor started but acted like it had a vapor lock. Continued to crack until engine turned over and started spewing a bunch of fuel out. It would run very rough after 5 minutes of mowing and then die in a cloud of smoke. 3rd mowing outing started the same way but would not throttle up to full power. I've removed, cleaned and replaced the carburetor now. Put in a new fuel filter, and verified fuel gets into fuel bowl. At this point it won't start and backfires after 30 sec of cranking. Please help with tips of what to check next.

How to Repair Small Engine Problems: Briggs & Stratton FAQ read through this & post your simplicity model number 7 digits.

Pull the dipstick and smell it. Does it smell like gas or above the full mark?

When I had the original carb on it I did notice fuel somehow flooded the carb and into the oil. I've changed the oil and filter since.

Have you checked the valve clearances?

No, I've only done the carb and fuel system troubleshooting. The plug also has plenty of spark.

Backfiring is normally a sign of any or all of the following. Excess fuel (running way to rich). Ignition at the wrong time (sheared flywheel key or air gap wrong). Valves opening at the wrong time (valve clearance wrong or bad cam lobe).

Results manual, parts list, wiring diagram.