Incorrect Timing Adjustment causing heat issues?

Dana67Dart said

Sounds like my 67 273 2bbl.

With vacuum advance on it misfires at around that same rpm. I'm at 5 before.

Spec is 5 after (CAP)

I checked the dwell and with the vac on it goes down way down and starts to misfire. Without the vac the dwell stays fixed and no misfire. Could be too much total advance? Could be dwell changing too much?

Click to expand...

I'd say dial a little out of the vacuum advance; either by increasing the spring load (takes more vacuum to move it) or limiting how much it can add.
With a CAP distributor, it was designed to advance so quickly that well before 2500 rpm timing would be essentially the same as a non-CAP engine.
So with 10* more initial than spec, timing at 2500 is 10* more than spec. There of course was some latitude (esp on non-CAP) to adjust initial a couple degrees for local conditions and fuel. But 10* apparently is a little too much.

Lemme see if I have plotted the 67 Plymouth 273 2 bbl timing curves.