I have a new Gen 1 small block with a Mallory HEI and Edlebrock intake and carb. Recently the engine has not wanted to run correctly. I have checked the timing, gas, carb, all the plugs look ok, but are 2 years oldand the wires are a little faded, but have no visible cracks. Most recently when I got the engine to run it idled at 1100, it would not rev past 3500 (unloaded) without a loud backfire. And after 5 minutes of idling the engine lost revs to 800 and stalled out with a slight backfire 2-3 seconds after the engine had stopped. My best guess is coil, but I am also considering the plug and wires. Any ideas?
Thanks for any help.

 

your on the right track, but also check for restricted exhaust like clogged cat