Engine continues to run after shutting her down?

[Mooch]

Hey everyone,

Chev 350, Holley dbl pumper 650 carb, stock fuel pump.

After I shut off my car, the engine continues to run, well turns over chugging over and over till it cuts
out and sometimes blows out air through the carb I believe. Runs from a second to 30 seconds at most.
Burning fuel left in the carb?

Or I shut it off while its in drive, and its chugs for a second or not at all.

How do I fix this?

Thanks 😉

 

[Peter]

sounds like dieseling. best bet is to start with some top engine cleaner and run it through the engine to clear out the carbon that may be in the combustion chamber. The carbon stays hot enough after running the engine for a while that it can ignite the fuel still coming into the engine. The top end cleaner (or seafoam) aims to clear out carbon from the engine and should help. but before using be warned it can also clean out things such as intake gaskets and stuff and cause more problems so use it at your own risk but many have used it with much success. An oil change after using it isnt a bad idea either.

 

[crotchss]

Check your timing make sure it's not too far advanced, should be around 12 BTDC. Also what is your idle speed set at? Too high of RPM at idle can cause run on also. Having the carb too rich and too hot of plugs can also mess with this.

 

[chevy2480]

Besides what was previously mentioned. Are you running a electric? If so i have seen and had one back feed electrical system and keep car running for a few seconds until fan stops. Try unplugging it from power source and see if problem continues.

 

[Bonnewagon]

All of the above as well as way too high of an idle can let enough fuel/air mix to sneak past and diesel. Around '73 GM added a solenoid to the carb so it would hold it open to run at idle speed yet close totally at shutdown so no dieseling. An MSD box needs a diode in the alternator wire because even 1/10th volt will support spark.

 

[larryo454]

Hi All of the above but if you are like me, i love more timing in a engine and it does the same so i shut my car down in gear.

 

[cutty]

i had that problem until i added ground straps from motor to body

 

[illregal]

a vacuum leak will do that too,it happened with my s10,spray your lines and around the carb base,and see if the idle changes

 

[LS1GN]

Mine does it when I run 87 octane - 91 or 93 it doesn't

 

[Mooch]

Thanks!
I'll give all these ideas a try during the week.
I dont have a tach so i dont know my rpm. I should get one soon.
It uses 91 octane.
Also one thing I do notice is when I shut it down and it continues to run, after it cuts
out the electric fan turns on.
So I'll try and figure it out during the week.
Thanks for the help 😉