Yo,
Check the ground wire from motor to chassis. Pull it and clean all contact points.
How many miles on motor? Timing chain jumped a tooth or two due to streach. Low compression? Slow cranking speed? Contaminated gas in tank? Plug Wires on correctly and on in proper direction of rotation?
Also check all wiring between Distributor/Coil and Ignition Module. Mine was all inside various wire looms and I had one wire that had come loose from a crappy wire crimp. It prevented it from firing