Hey I'm new to this but I thought I'd try it out. I've got '71 Ford highboy I replaced the original 360 in it with a 460.a few years ago. Lately when I shut it off it wants to keep running I believe it's called spark knock. It don't do all the time. I've moved the distributor a little in both directions but nothing seems to help. I'd appreciate any help someone might have.

 

I believe it was called "dieseling or run on".
I also believe they used an idle stop solenoid mounted on the carburetor that when the key was on it idled at normal idle speeds. Then when the key was turned off the solenoid would drop back and close off the throttle plate thereby preventing it from getting any air/fuel and preventing it from dieseling.

 

throttle solenoid solution in the previous post will work. if you have an auto trans, you can try keeping your foot on the brake when you stop to park and leaving the transmission in "drive" while you turn off the ignition. this will load the engine down and keep it from dieseling. you can also try running the next higher octane gasoline. if your idle rpm is adjusted too high, it can contribute to dieseling occurring or make it worse.