I have a 28R707 13.5 hp engine
I had gas dripping into the oil reservoir and when I started it up I had a lot of black smoke. I drained the sump added new oil and all was fine but it happened again. I put in a fuel shutoff valve and all was working great. It was running great until recently when I stopped to remove the grass and it would not start. I checked the spark and it looks fine but the engine will not start even with fuel added to the air intake. A couple of times I got one ignition but it blew through the air intake.

Do I have an engine problem? What should I check next?