[chevellemalibu67]

Why does my chevelle diesel when i shut it off. Its 327/350hp with a 650 holley, nothing special really. When its warmed up and i shut it off it diesels and it mostly does it around people which angers me. Give me some pointers on what I should do/check. Thanks.

 

[Mike]

Throttle blades too far open and/or timing too far advanced.
GM put a throttle solenoid on some cars to allow normal idle but would completely shut them with the key off.
You might try that if it's not the timing.

 

[Tom Mobley]

what is the idle speed?

 

[oldtimr]

heat, load, air, fuel.

decrease heat, air and/or fuel

or increase load(leave it in drive when you shut off key)

Timing is not part of making an engine with the key turned off stop. Once the key is off spark ends.
Dieseling occurs as CI (compression ignited)combustion, contrasted to SI (spark ignited).

Retarding the timing lowers the rpm(and air/fuel flow). Also makes it run hotter(oppoisite of desired).

Just venturing a guess.....Probably running on ported advance and have the butterflies open too far to get decent idle rpm to compensate for retarded timing. If so, go to full man vac adv and then you can close butterflies down and get back in the idle circuit, reducing air and fuel flow and also cooling the engine. Or get the dam 190 stat out of it and put a good ole 160.

 

[Mike]

Tim ,wasn't meant that the timing was causing the dieseling but that the timing was causing the need to increase the idle by opening the throttle blades too far.
Cause and effect.

 

[chevellemalibu67]

The rpm was 900-1000 but i think the electric choke was kicking on so thats why it was raising it cause we set it at 650-700. We adjusted the choke and idle so ill take it around the block tommorrow and see what happens. The timing is right cause I just put a pertronix kit in it so we had to reset the timing.

 

[oldtimr]

Mike, I didn't think that's what YOU meant. But lots of folks DO, and all I attempted to do was submit the actual causes/affects. Sorry if I came across wrong Mike.

 

[charbilly2001]

Why does my chevelle diesel when i shut it off. Its 327/350hp with a 650 holley, nothing special really. When its warmed up and i shut it off it diesels and it mostly does it around people which angers me. Give me some pointers on what I should do/check. Thanks.

Until you get it figured out shut the car off in gear ( automatic) or leave it in fourth and let the clutch out as you turn the key off. That'll save you the embarrassment.

 

[SWHEATON]

Just becasue you jus installed a pertronics ign doenst mean you have base & total timing right,so what is base timing with motor idlng low at 600 rpms with vac adv unhooked and plugged?

Whats total timing too?

Anyway,it's Usually its retarded base/total timing heating up the motor that causes desieling/run on,not timing being a little over adv as was suggetsed.

So esnure you have a least 16-18deg base timing if running a non gm aftermarket cam .

Also look for 36-38 total.

Lean idle mixture and or lean fuel calibration in general can add to run on issues too.

Motor running too hot or idle speed too high can also add to the problem.

A motor thats too carboned up wil also do this due to carbon getting red hot and actually firing incomming fuel when the ign is shut off. A motor can get too craboned up from using oil and fuel calibration too rich.

Motor needing more octane can also run on when shut down too.

Too hot of a spark plug heat range.

Some of the above mentioned items wont make a motor run on by themselves but collectively 2-3-or even 4 of these issues together like lean idle mix/retarded timing/low octane fuel/high idle speed can collectively cause run on .

Scott

 

[chevellemalibu67]

I might have figured it out. The electric choke is bad. It was sticking even when it was warmed up, id kick it off but it would gradually come back on so I just disconnected the wires and so far so good. Who needs a choke anyway.

 

[Jerry70]

I might have figured it out. The electric choke is bad. It was sticking even when it was warmed up, id kick it off but it would gradually come back on so I just disconnected the wires and so far so good. Who needs a choke anyway.

If you just disconnected the wires without adjusting the choke to full open it will stay closed all the time.

 

[SWHEATON]

Well the choke not comming off all the way with high idle steps still raised/activated effectively = the idle too high to me which mult people mentioned as a possbile cause for your run on problem.

Idle too high is idle too hgh no matter how you cut it./LOL!!!!

But either way you still need to get whatever is the issue with the choke corrected.

Scott

 

[chevellemalibu67]

If you just disconnected the wires without adjusting the choke to full open it will stay closed all the time.

I did adjust it to full open. O and the idle is set at 700rpm.