1980 Ignition
 

I finally got my 80 with Weber to idle and run OK. I did find that when I pressed the break pedal the damn thing would have a lot of pulsation even though I replaced every part on the breaking system and all the bushings.... So I have been looking for a while and finally found the problem- bad idler arm bushings. SO now I'm replacing that. Now a question:

The car seem to run and idle well until yesterday. I started it up and it is backfiring a lot. So I took the timing light and timing was good. Now, I have a half bridge running at 1500rpm idle and I set it to the yellow pulley mark on the leading and the red on the trailing. Should I retard timing at 1500rpm idle? I tried advancing and retarding timing and still the backfiring continued. I put the timing light on all the spark plug wires and three of them flash rapidly when the gun trigger is pressed, however the leading rear rotor flashes slower than the other three. So now, the question,

What could lead to erratic firing of the spark plugs? Coil, ignition box, wires? How do I isolate the culprit- the wires look pretty new and terminals are clean...

Thanks

Are you using the stock 80 ignition box? It does some funny things at certain RPMs and temps to the ignition like delaying spark and turning it on and off. You can read up on it in the FSM.

The 1980 was kind of unique. It was an attempt to make it electronic. Best to swap to a 1981-1985.

My big concern is that 3 of the 4 spark plugs will fire very fast and only the rear leading is firing slower. Could this be the cause of the misfire? The rear leading is definitely not firing as evenly and fast as the other 3. What would it take to swap to the newer ignition?
Thanks

It would take a 1981-1985 dizzy with igniters and dizzy harness. I THINK that's it. This would do away with the points dizzy and 1980 igniter box on the stock tower.

Misfire or delayed fire on the leading could definitely cause backfire (actually, afterburn) by dumping unburned fuel charge out the exhaust port, or firing late when the port is opening.

IF L1 is firing reliably but L2 is not, the place those signals split up is at the distributor. Everything else in the leading ignition is common to both L1 and L2 firing.

Check your cap and rotor internals, and make sure the cap is seated squarely. A fried or corroded terminal inside the cap could be preventing reliable L2 firing. Likewise test your L2 cable by temporarily swapping it (both ends) with L1.

The 80 ignition box is kind of prone to crosstalk on the pickup signal wires, especially if the noise-reduction capacitors ("condensers") have degraded from age or if the shield connections are dirty, but this usually shows up as early fire on the trailing, not on the leading circuit.