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Rough idle in gear

The stock points distributor set-up is not designed to last running full system power of some 13 vdc. Maybe Mid can give a expert explanation of why the stock system was built with voltage reducing resistance in place.
My suggestion to you is to dump the stock ignition set-up and move up to a more powerful and reliable electronic version. For SBFs many turn to something like the Pertronix stuff. That's what I put in mine (and yes, I have no street time) but it fires things very nicely and has built in stuff like multi-spark and a rev limiter too.
 
This was while cranking only. The pink resistor wire only drops the voltage while the engine is running (key is in the ON position).

This test was only performed to test the existing wiring, and I don't intend to bypass the resistor wire and run full voltage to the coil all the time. I suspect that I will find a problem with the wiring under the dash or from the firewall to the coil.
 
Removed the condenser and tested it with a new multimeter today. It seemed a little flaky so I bought a NAPA/Echlin condenser (they didn't have points in stock, so those will be replaced soon too). Testing the 2 side-by-side (check resistance to build up a charge, then switch to measure voltage to watch the discharge) didn't appear much different to me, but my son said it appeared that the new condenser discharged more slowly than the old one. Popped it in and the car fired right up with a nice, smooth idle - hasn't done that in a while now. I let it idle for probably 15 minutes, occasionally revving it. Adjusted the timing again for the highest vacuum and then backed it off a bit. I think I'm at about 10* BTDC now with 20 in-Hg - that's a bit more advanced than I've set before, but it seems to like it. Hope to be able to test drive it this weekend, but I am pretty optimistic that I found the culprit.

Boy, I sure made this harder than it needed to be. :( I assume a flaky condenser would also explain the varied sparks I got from the coil and plugs, which I attributed to other potential causes. I really wanted to avoid just throwing parts at the problem until something fixed it, so we spent a lot of time trying to test various components. But now we have a rebuilt carb, a spare starter solenoid/relay, and a spare coil. Everything that was wrong was related to the re-man distributor I bought a while back - vacuum advance was misadjusted, points needed cleaning and adjusting, and the condenser went bad. At least we learned a lot.

Thanks for all of the support!
 
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