A simple thing to check: Is the spark plug wiring 180 degrees out of phase, backwards?
I made that mistake the first time I wired mine up and it did that. Backfires, spitting but trying to start. The distributor spins clockwise. I thought it went the other way. I was convinced I was right and it took days to finally realize my error.
On my 50/50 chance of getting it right, I lost.
It's just a thought.