has spark and fuel, wont start.

Get a volt meter and find out where you do or dont have 12 volts. Here's why...
The large positive battery cable and a good battery will spin the engine fine but that wire doesn't power the car. A problem in the alternator, ignition switch, bulk head connecter, etc.. can produce voltage drop.
The ballast resistor is proof that the engine will run on less that 12 volts. The way the ignition is wired to bypass that resistor in the start position is proof that the engine needs 12 volts to start.
An engine that is tuned fairly well will start on the weaker spark if you block the choke open and feck with it long enough. Hours or days later you're back to square one. That is very likely the change in resistance at the bad connection that comes from heat and movement.
Quite a few of my IVR customers while reporting there gauge faults will state that the amp gauge twitches violently with the trun signal flash. There's your sign of a weak electrical system. Hope this helps