Advance adjustment(s)

I had/have the same problem with the mystery 340 I bought and put in my swinger (I call it a mystery because I do not know what cam/compression it has and it basically came to me as a 2,000 mile crate motor.

I believe the distributor is a stock Mopar part (based on the part number), but I have no idea what the springs are. I found that the issue goes away if I run the motor hard for a few minutes and then park it, as it idles fine right around 700-800. However, if I rev the motor in neutral it will let the idle creep up to 1,000-1,200.

I wonder if I'm having the same issue with the springs that you have. Waiting for somebody more experienced to chime in here.

Thanks for posting.

-Mike