So my brand new 454 is getting a little run-on. Meaning when I turn the engine off, it still sputters and then dies. It has low compression and I use good gas. I was told maybe the spark plugs aren't hot enough. Does that sound right? Or is it something else?

 

Don't think too cold a plug would do that. Maybe too hot of a plug.

I've heard that if the spark plugs are too long, the threads will extend into the combustion cyl and cause hot spots, which can cause run-on.

Idle speed normal??

 

Have you checked your timing??

 

westman where in boise are you? I live in caldwell but work over in boise on overland.

usually run on is caused by something being too hot in the combustion chamber on a carbed car. either too hot of spark plugs, not enough coolant in the system, carbon build up, sharp edges in the combustion chamber or timing issues.

 

Timing seems to be good. ZZ28ZZ has me thinking about the plugs. The engine is the new Gen VI originally set up for TBI. My set up is carbed with HEI. I compared the plugs from the gen VI to the old Mark IV. The newer Gen VI are much longer than the mark IV and call for a .60 gap instead of .45 . The engine is brand new with only about 2000 miles on it. So there shouldn't be any problems with cooling or carbon build up. The heads did have a port and polish job done. But its a reputable shop, I can't imagine them leaving something sharp.