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.

 

Can't say for sure from here, but yes, the key can be a problem, so I would try that before going any farther. I always use an OEM key, because if something does break, it's better that it's the key, not the flywheel. Is this on a lawn mower, and, if so, do you have the blade installed?

 

No it's on a dethatcher. When I got it it wasn't running and had been left outside for a few years. There was water in the crankcase and the choke was full of rust from the air cleaner housing rusting out. The key is a bit wider than longer so when I put it in it is snug in one direction but not the other.

 

The key is critical for maintaining the timing and even a partially sheered key can let the flywheel rotate enough to cause trouble. You should still be getting a spark regardless.

Since you have gotten spark and have manually added fuel and still the engine won't sputter or run for a second I'm wondering about the compression. How does the cord feel when you pull on it? Does it get hard to pull as the engine comes up on compression? Do you hear any bad noises when you pull the cord? Have you adjusted the valves or even seen if they are moving?

 

The cord pulls with the normal feeling, there seems to be good compression. The key is not sheared and it keeps the flywheel in place but as I mentioned there is ply in the flywheel until it is tightened down. I don't hear any bad sounds and I have not looked at the valves but since there is compression I am assuming that they are not stuck.