Ok, I removed the jumper so the MSD is only hooked to the leading coil and I hooked the trailing coil back to the stock connections. The MSD is hooked up to one of the ignitors (I cant tell which because all four wires go into the harness below the coils). The tach is working again but now I have a slight knock. Timing is off? Thanks for the help. These mods were all done by the previous owner and I have no experience with them. By the way, now that my tach works again I noticed the car idles rather high, normally so with a holly carb and aftermarket fuel pump I understand, but what kind of RPM am I looking for? And where is the idle speed adjust screw?

If you want bigger spark on your trailing ignition, you have to use two separate boxes or step up to a high dollar digital ignition. The MSD mod causes the leading ignition to fire on both the power and exhaust cycles (called wasted spark). This has a side effect of cleaning up your exhaust, but also simplifies your ignition. Your trailing timing and combustion chamber shape are not compatible with wasted spark, and thus the two rotors must have separate ignition.



Your leading timing should be between 24* BTDC and 0* while your trailing ignition should be 8* less. Use a timing light to see when your spark is occuring. If your leading ignition has less advance than your trailing, swap the connectors to the trailing ignitor.

Oh yeah, my setup is as follows: Half-bridgeport 12A, dual Weber 36DCDs, a very open exhaust, MSD 6A and 2nd gen coil on the leading ignition, stock trailing ignition, 24* leading, 16* trailing, lightweight steel flywheel, and I still idle at 800rpm. I attribute it to the intake setup's previous owner doing a ton of tuning. I know very little about carbs and haven't done any Holley tuning.