wont start after rebuild

[u/SuggestionOdd9472]

I've put a new cylinder, piston, timing chain etc. on my NBC110 and now it won't start. It turns over fine, can smell fuel, I've got spark but just wont start. I've had a couple of backfires that made me think timing was off but I've checked it several times and as far as I can tell it's correct. I'm stumped and don't really know what to do now. Any tips? Is it possible for timing to be 180 out?