have an idling issue with my 283

[CRGRS 66]

my 283 is idling way too high (sorry, no tach), and this is a new problem, nothing has changed. I tried backing off the idle adjustment screw, and the spring is plenty tight, no change. I disconnected the throttle linkage, thinking maybe something was binding, but still no change. When I got home tonight, from a relatively short drive (10 minutes ish), there was some smoke from under the hood (not a lot, and not thick), which quickly dissipated after I shut it off (at which point there was some brief run on). The temp gauge was where it always is. Carb is a 650 holley single pump, not sure how old it is, but it is quite new looking.

Could this be a timing issue? have not checked the timing yet. Maybe overly advanced timing might leave excess heat in the heads...