I have a 340 with the Mopar electronic ignition. I went to set up the timing at 35 degrees total without vacuum advance, and noticed that when it got to 35 degrees at 2200 RPM, the timing was moving around between 35 and 40 degrees. Could this be my timing light or my ignition? Thanks.

How many miles on the timing chain? Worn distributor, perhaps?

Give this a look.

http://www.cuda-challenger.com/cc/index.php?topic=61037.0

Had a similar problem with my old 64 300, the dual point distributor was all wore out. A new distributor fixed that.

But it could be a few other things. I'd check for chain slop. Never had to use a collar to get steady timing.

timing gears/chain or needing a collar on the dist shaft or both.

I just went thru this with my 440 for over a year. This is what I found. The gap at the reluctor way like 18 thousands and the thing had two very lite springs in the dist. which was causing it to advance way to soon. Left one light spring in and put one heavier one in and set the reluctor at 8 thousands and the timing and idle is great.

Thanks Moparts