I've had the same set-up for years with few changes: Indy SR-headed 440, with Mallory/Hyfire 6AL ignition box (mounted under the hood), MSD coil, Mallory distributor. The only recent change was a couple of months back when I swapped out my 0.031" Holley squirter for a 0.035" squirter to help with a slight off-idle bog (I don't believe that this is the culprit).
The car has been having some kind of strange starting issues lately. The battery will seem near-dead after sitting for a few days, and will sometimes die before I can get the engine running. The battery's only 4 years old, and didn't seem to have any issues when I recently put it in my truck.
Out of the blue, the engine started backfiring through the exhaust yesterday. At first, I thought that it was loose plug wires, but they checked out. I also pulled all of the plugs and the distributor cap, but everything looks good. I tested the coil's resistances and they were 0.8 ohms across the primary and 7500 ohms across the secondary (higher than the advertised 4500 ohms).
I could be wrong, but I'm convinced that it's an ignition problem. Other than the backfires, the engine seems strong while running with the car in park. The backfires aren't consistent. If I bring the engine up to about 2500 rpm I'll get a loud backfire about every 30 seconds.
Any idea what I should check next? ...pull the valve cover? ...check compression?
Thanks in advance for any help?