Post 12
Those rotors can burn through letting the spark jump right to the metal advance assembly underneath.
From the looks of the button in the cap and the metal contact on the rotor the spark has been jumping around a little.
With a problem like that the spark gets forced to find another path, and does as you add load to the motor.
Most people don't realize it but the higher the cylinder pressure goes, the harder it is for the spark to get to and jump the plug gap.
And especially with HEI it WILL find another place to go.
Normally on that type of distributor that is straight down through the rotor.