maybe a ballast resistor, if your HEI was working fine though then that shouldn't be a problem.... crack in the dist cap maybe? that'll scatter your spark sometimes to the point of no spark also is it an in cap coil or out of cap? if its in cap make sure your bushing and contact between the coil and rotor are properly installed.... also you can send the coil to dist wire to ground, should see some nice spark of the coil is getting spark if not, then its time to check the trigger