question for I/O guys

[spareparts]

go back to basics, check compresion, you've checked fire, but put an inline spark checker( the neon one) on it and see if its sparking under compresion, then use a "small" amount of starting fluid to see if its a fuel deliver issue.

One other thing, did you loose the exhaust flapper in the pipe, they can get sideways in the pipe and create a lot of backpressure