sounds like a compression issue to me. Check compression should be at least 120. I would bet you need rings or crank seals.
spray a little starting fluid in the carb throat and see if it will fire. If not I bet compression is the issue. Next step is a leakdown test.
I agree I had the same issue with a Polaris 400L Spark but not fire. Compression was crap. But try the starter fluid idea anyways. Best way to know for sure if it is a fuel delivery issue or compression.