Runs great until it heats up

Welding with battery connected or even disconnected but with you electronic Mallory still connected isn't good. They probably killed the module in your distributor. My two cents.

Brother just did the same thing last race season on his gasser Falcon and killed his MSD box. It would crank and run, but act weird under load. He figured it out AT the track...
 
tubman said:
Run aftermarket electronic ignitions at your own peril.
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Mr tubman, exactly my sentiments. Although I have pertronix units on my early falcon and mustang for many years and no issues. They are easy to change back to points/condenser on the side of the road. Regards, Kevin.
 
Both idling and under load, but more pronounced under load. Haven't ruled out vapor lock. I did rule out the ballast resistor for the coil. I put a new one on, problem continues. Coil is hot enough when I got back to cause me to take my hand off of it really quick.
 
Coil is hot enough when I got back to cause me to take my hand off of it really quick.

Looks like you are on the way to a solution. You've still got a problem with the mismatch of coil/resister.
 
srg said:
Both idling and under load, but more pronounced under load. Haven't ruled out vapor lock. I did rule out the ballast resistor for the coil. I put a new one on, problem continues. Coil is hot enough when I got back to cause me to take my hand off of it really quick.
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What is the voltage at the coil, points open and points closed. G.M.
 
srg said:
Both idling and under load, but more pronounced under load. Haven't ruled out vapor lock. I did rule out the ballast resistor for the coil. I put a new one on, problem continues. Coil is hot enough when I got back to cause me to take my hand off of it really quick.
Click to expand...

What ballast resistor and which coil are you using?
 
No point in just guessing here and swapping around parts, you have to do some testing with a meter because your coil should not be that hot. Its hot because its drawing too much current. Measure the coil primary resistance in ohms and also the resistor which should measure up to a total of approx 3 or 4 ohms. Another way is to measure the current draw of the coil with the engine running at idle speed. Should be no more than three amps. As you rev the engine up a little the current draw should lower to maybe two amps. Regards, Kevin.
 
koates said:
.....engine running at idle speed. Should be no more than three amps. As you rev the engine up a little the current draw should lower to maybe two amps. Regards, Kevin.
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Kevin, can you explain this to us wanabe electrical geeks? Why is current draw less with slight increase in RPMs?
 
Jay, The distributor contacts or the electronic switching pick up (on an electronic ignition) in the coil primary circuit act as a kind of regulator by rapidly switching on and off and the more engine RPMs you have then the faster the switching cycle and therefore the lower current (amps) draw in the coil primary circuit. That is also how a voltage and current regulator works on your cars generator circuit. Hope you can take in that explanation. Regards, Kevin.
 
I had a similar prob early on when going w a New engine that was supplied w a resistor mounted to the Engine engine next to coil. Not thinking about it I hooked up the ignition circuit mounted on engine to the stock wire on the wiring harness for the ignition. I didn’t take into consideration that that wire already had the under-dash stock resistor in the Car wiring circuit so ended up w current going thru both resistors causing a similar problem SRG is having. Eliminated the under-dash resistor & problem disappeared.
 
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