My '54 Chevy 3100 truck has new build engine, new fuel pump, cleaned gas tank with vented cap, new fuel filter and is getting gas to the carb. It will start, run, then die out. There is power to the new internal resistor coil, power to the distributor. Condensor is tight. New plug wires and plugs.So I am guessing that the only thing missing is spark. What could cause spark to go away intermittantly? Help. Thanks.