Pop pop on exhaust side

Chadderbox,
Maybe I missed it. Are you using a MSD 6* box? If so, I do not believe low voltage would be the cause of the problem. The MSD instructions clearly state that it will deliver full voltage with a 9-18 supply voltage & will supply voltage with as low as 5 volts.

If you have a MSD RTR dist & are using it to fire the coil. That is an inductive ign system & they ARE voltage sensitive.