[RichardJ]

If your problem is overheating at idle, what do you care what the timing curve looks like at 3000 or 3600?

800 rpm is not idle rpm unless you have a big cam.

At 800 rpm the throttle blades are opening the transition slots and you really can't adjust the idle mixture screws.

At 800 rpm, most stock distributor curves have already begun to advance and you can't set your base timing. You mentioned softer advance springs which could be problematic, at least until you get your other problems sorted.


You need to get the idle down to 600-650 rpm.
For now, remove the vacuum advance hose and plug the carb port.
Check for vacuum leaks.
I'd put a radiator pressure tester on it and make sure the system holds pressure.


>>gets harder to time the longer the truck sits with the fans running, seems to get really hot when running the timing procedure.<<

What do you mean by "gets harder to time"? "timing procedure"? You turn the distributor until you reach the base timing that you want and then lock it down.

>>Tuned AFM to highest steadiest vacuum with a vaccum guage - best i can get at most timing settings is 16-17.<<

Is AFM supposed to be an acronym for fuel mixture? Does the "16-17" mean inHg or base timing. i can't tell for sure.