460 looseing spark after warmed up

I have cobra kit car with a 79 ford 460 in it nothing to fancey, i am running a mallory distributor with a msd blaster coil , reason why is, i was running the mallory coil without a balast resistor and she cracked open. The car starts right up, i pulled the wires and checked the spark and it was cracking prety good, i ran till it warmed up and then is started missing, i pulled a wire to check the spark and it was no ware near the spark it was at when i first started it. The coil is maybe 2 months old. What you think.

It's a good place to start. Plus the fords are suppose to have the resistor wire going to them, unless your new ignition system is designed not to? My 460 has a internal resistor built into the (mallory)coil, so I wouldn't have to put an external one on the block or firewall.

I installed the ballast resistor befor i put the new coil on

How are the old wires? And have you checked your timing? Any lose vacuum lines? Just guessing here. Good clean heavy guage grounds to frame and block?

Wires are new, timing is good,vacs are good and ground is good. Runs perfect until it gets to opperating temp.

I had a friend whose motorcycle ran great until it warmed up, then it would shut down. Drove us crazy trying to figure out what was wrong with it. Turned out his condensor needed to be replaced. Sometimess warmed up cars have choke problems too. Maybe some other guys will chime in with their thoughts.:rolleyes: