1980 C10 Running but weird to stop

[JamesDeRabbie]

Been picking away at this truck and since I got it, it runs and drives fine, but if you try to turn the truck off in park, it continues to run in a rough and sort of sluggish state. Now if you put it in neutral and turn it off, it works every time. Ideas? This isn't a deal breaker on the truck, but id definitely like to figure out what's going on with it so I can fix and not worry about it.

 

[legopnuematic]

Sounds like you are experiencing dieseling.

What does the truck have for a carburetor? Quadrajet? Carter/Edelbrock, Holley?

What is the base timing at?

Late timing (retarded) will require the throttle blades to be open more (idle screw) to bring idle up. When the throttle blades are open too much at idle, it can lead to dieseling among other issues.