With you having spark, I assume gas is getting the spark plug wet, compression and spark
now, all that appears to be a likely issue is the timing (which has to be dead nuts on).
Checking the valve opening and closing, we're trying to confirm valve timing is correct.
Coil to flywheel to crankshaft as well.
Now something not addressed, on the crankshaft(near the sump) is a removable KEYED gear
That gear can come off (and does normally). That gear meshes with the camshaft and times the camshaft to the flywheel. If that key sheared, cam to crank timing WILL be off....
Shown here on my 18 HP Briggs: