Sputter after shutoff

[sleepery]

My engine sputters after I turn off the key at times . High octane fuel helps it not to happen . A guy told me to keep the brake pedal depressed while turning the key off and it worked about half the time . What causes this ?

 

[Quest]

what kind of car you talking about?

Carbed or EFI?

 

[sleepery]

It is a 1978 Chevy Van with a 292 6cyl . I think it has a single barell carb . Engine taps after 5 minutes or so and and it smokes for a second or two on startup occasionally . I use those "non-fouling" type plugs lately to keep it from stalling . Just looking to keep it running as long as it can . It is used for work doing short trips .

 

[Quest]

Usually it's a sign of one or more of the following:

(1) excessive gasoline remains inside the combustion chamber even after shutoff, causing "auto-ignition" (similar to dieseling due to compression ignition) even after you turn off your engine.

(2) carb is out of adjustment somewhat.

(3) air filter is a bit clogged, causing the carb to run a bit rich.

or a combination of 1 or more of the above.

Usually, if it's the older, pre-cat days cars with carb usually tends to over-run a bit even after shutoff and this is fairly normal and there's nothing I would do to it (doesn't bother me at all).

Q.

 

[Rabbler]

Engine probably has a bunch or carbon build up in combustion chambers.
Go by a couple cans of combustion chamber cleaner and run it down the carb.
Make sure idle speed isn't set too high.

 

[sleepery]

Thanks for the replies .

 

[punisher]

Chances are the throttle kicker/anti diesel actuator are shot. Not all carbs have them.

 

[tomcat27]

yup. that was a common problem with the later carb'd cars and some boats - with the combination of carbon buildup, high underhood temps, etc. the term was called "dieselling". you can look into removing the carbon, check the throttle kicker, and also simply shut the car off in gear (if its an automatic). the extra drag of the torque converter will usually keep it from dieselling.

 

[mechtech2]

Your idle speed may be too high - check that first.
But turning it off while in gear will cause it to STOP - right now.

 

[chrome]

Some carbs have a solenoid switch shut-off which cuts fuel flow through the jets when the ignition is off. If this switch is faulty, then fuel may still be drawn through the jets during the last few revolutions. This in conjunction with carbon buildup may cause the running-on symptom.

 

[ffhdriver]

This was a common problem in the '70s cars because enviromental changes to the engine were in a learning mode. My '76 Pinto did it until I installed a solenoid to shut the throttle and lower the idle speed when the ignition was off. It was called "dieseling" because the engine ran with the ignition off.