I waited for someone to bring up the solenoid.
That truck never had one or, at least I never saw one any of my 70's big GM 366 or 427 trucks.
But I think getting one will help.
Look for 70's GM cars and light trucks with AC.
They were used as a fast idle solenoid while the compressor was engaged.
What you can do is back the idle screw out so the butterfly completely closes.
Then drive the truck, Remembering you have no idle, so you will have to give it a little to keep it running at a stop.
The goal here is to completely warm the engine.
When back home, try to idle the truck as close as you can with your foot.
Then turn off the Ign. while lifting your foot at the same time.
If it dies correctly proceed hunting a solenoid and it's bracket, If not I guess we need to
Keep looking for the cause.
I agree with the other post's about 99% of the time run on is caused by fast idle, Vacuum leak, or rich condition.
Yes carbon and timing can contribute but only in a small percent.
My 74 C65 with 427 never runs on, or the 64C80 with 409 either.
I wish I could give you a direct cause for your problem.
Good Luck
Tom
Thanks for the input, Tom. As you can see in the video I posted, the truck will barely 'run on' with that low idle -and sometimes it won't as indicated in the first 45 seconds of it. I believe that Jerry's solution is the way to go for my situation.
I really do appreciate everyone's advice and willingness to help.
