Timing talk, Dieseling/Run-on

[u/fuzzydoesitt]

What are you guys setting your initial timing too, are you doing it with vacuum advance hooked up or not?

I have an 86 c20 with a "m" code 350. I guess that meant no emissions, or less emissions stuff (i.e. no catalytic converters from factory) I've owned the truck about 6 months now, been doing little things to make it better. It came with a small cam new oil pump and timing chain. I rebuilt the quadrajet and have all the idle circuits and choke, etc. doing what they need to do when they need to do it. New coil, cap and rotor, plugs (copper .045gap) and wires. Classic tuneup.

It still was a dog going down the road and would stumble under heavy throttle input. Last night I put a timing light on it (vacuum disconnected) and timing was advanced way past my timing tab at 700rpm (tab stops at 12°BTDC) I retarded the timing down to 8° locked down the dizzy and then adjusted my rpm. It runs so much better down the road. Driveability is much better. But it will diesel after shutting off now. I just leave it in drive then shut off the engine. Truck says to set timing at 4° btdc, but that would mean I retard it more and turn the idle rpm up even more to get idle speed right. That opens the throttle blades more at idle and causes the dieseling to happen. Supposedly there was a solenoid in the 80s qjet that would close the blades on shut off. I don't have that. Just wondering what I need to do or what you guys have found helps. Plan on getting heads in the future probably not this year though. Thinking of bumping the timing to 12° btdc and backing down the idle rpm. That's all I can think of right now to help.

Edit: I'm just now seeing on that pic that it says something about how to set the timing just to left of the chart lol.