The carbon rotor button in a stock HEI distributor cap has very high resistance. When the high voltage of an MSD 7-Series Ignition is added, this resistance builds up heat and can actually melt the distributor cap. The solution to this problem is the use of the MSD Low Resistance HEI Bushing which will pass the secondary voltage from the distributor cap to the rotor without excessive heat buildup...
Let me help you spend some money :)