Incorrect Timing Adjustment causing heat issues?

jau126 said

they apparently adjusted it because it was “misfiring” at around 2500 rpm

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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?