Just tried to depict the 'very simple' requirements for engines to run. If theres a leak and u hit your leak with starter gas, then it should sputter. If no leak, no hit...

Spark really comes on time? Injectors click'n spit as u rotate cam sensor with finger while ign on? Enough rpm during start, voltages ok in all places?

The most 'impossible' problem for me was when I drove the -43 Jeep, without any problems, to garage: on its LAST REV the chain jumped... After 2weeks, plastic bag on carb visualized sucking-blowin-sucking-blowin etc during crank. Say NO! to blowin...