Tuning Question

[Dashman]

Are you using the original coil power source? Because that wire has a resistor built into it near the bulkhead and does not supply 12 volts to your HEI distributor. Just a suggestion because you didn't say how you supplied power to your HEI distributor.

Also check the vacuum advance unit that it is moving freely, or moving at all, and it goes to timed port vacuum, not manifold. Manifold vacuum would be advancing it when the RPM is decreasing, no bueno.

You could be slightly rich in the idle to mid range RPM.

Research key words "backfire, carburetor, and tuning". I have come across some great articles that helped me when I had carburetor issues. It's been so long since I've had issues that I can't remember what were the solutions.

One last thing, what elevation are you at? The jets could be rich throughout the RPM range.