2-cycle starts but only stays running by throttling between choke and full.

it's got a Briggs 4.5hp - about 7/8 years old - rebuilt the carb 3-4 years ago - after use it smells of gas for 2-3 days. I don't remember this being a problem when I rebuilt a few years back - I think surging was the problem then. TIA

I have a 3 hp Briggs that won't start. I have spark but I'm not sure if that is still not the problem. Here is what is happening. I pull the plug and lay it on the head, pull the cord and I see a spark. I put gas down the cylinder replace the plug but it still won't start (it does seem to possibly backfire a little but I'm not sure). Do the same thing with another plug and starting fluid still no start. I replaced the coil with a used one (condition unknown) and got the same results. Spark but no start. I removed the flywheel and sanded the rust off. When I reinstalled it I noticed that it was a bit sloppy but is tight once the starter is tightened down. Could the shaft key be worn causing the timing to be out? The shat key only fits in one direction and doesn't seem to completely fill the slot in the shaft up and down.