Engine/Carb shutoff question...

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Sep 1, 2006 | 10:43 AM

SmokedTires

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Le Mans Master

Joined: Apr 2000

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From: B'Ville NY

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St. Jude Donor '05

Engine/Carb shutoff question...

Hi all, I have a question about when I shutoff my engine. It seems like whenever I shut it off, the engine has to take one last big breath before coming to a stop. I turn the key to the off position, and the engine will rev up and then stop, not dieseling where it still trys to run. I know I still need to tune some more, but this has me baffled

Idle is set at 1000rpms if this helps

Sep 1, 2006 | 12:36 PM

builder

Burning Brakes

Joined: Jun 2006

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From: South Dakota

idle down

try turning your idle down.

Sep 1, 2006 | 01:26 PM

SmokedTires

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Le Mans Master

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From: B'Ville NY

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St. Jude Donor '05

If I turn my idle down, the car stumbles when taking off from a stop. The accelerator pump trickles fuel as soon as the throttle is started to move. Its not too lean, because it will burn your eyes if you're too close to the exhaust fumes. My narrow band O2 sensor says I'm just on the rich side of stoch, but it does run rich at part throttle cruising that I need to correct yet. I also up the jet size which helped a part throttle stumble when accelerating.

The rev-up when shutting off is a new one to me.

TIA

Sep 1, 2006 | 01:46 PM

Ironcross

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From: Taylor Michigan

By all means turn the idle down, fuel dragsters dont idle that high. The run on may be caused by the fuel in at cylinders at shut down with the 1000 idle. Not specific to your engine but the bog may possibly be cured by a slight timing advance and that will clean the engine up and then turn the idle back down. Bogs however may be caused by carb problems too. Hydraulic performance cammed engines are good at 600 and solid lifter approximately 200 more for a reasonable idle

Last edited by Ironcross; Sep 1, 2006 at 01:49 PM.

Sep 1, 2006 | 04:02 PM

Z-man

Race Director

Joined: Nov 1999

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From: Foxfield CO 1970 Convertible

Accelerator pump, jet size...I thought you had FI???

I agree that 1000 is too high for a warm idle. When you turn it off, just the momentum of the moving parts will make it continue for a while.

Another thing to check - when you turn off the key, do the throttle plates completely close? They need to close all the way - no air leaks at all - not even a smidge. My carbed engine used to stop immediately when I made sure there was no air coming in...

Sep 1, 2006 | 04:41 PM

BigBlockk

Drifting

Joined: Sep 2004

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From: North Bend Ohio

What is your initial advance set at? Retarded initial advance will cause you to open up on the idle to keep the engine running.

BigBlockk

Later.....

Sep 6, 2006 | 03:16 PM

SmokedTires

Thread Starter

Le Mans Master

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From: B'Ville NY

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St. Jude Donor '05

Sorry I didn't get back sooner. I took the kids to Boston to see the New England Aquarium and the Childrens Museum, then it was a drive to visit Santa at Santa's Workshop at the North Pole just north of Lake Placid in NY.

Thanks everyone, I'll be trying all of you advice the next time I play with the vette. I raised the idle to 1000 because the engine wanted to die when I came to a stop with a 800rpms idle. I'll check the timing again and see if I can get it to idle at 800rpms.

Sep 6, 2006 | 03:26 PM

rastadr

Pro

Joined: May 2005

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From: Miami Florida

i had this problem when i installed the msd 6al box. the cure was a diode into the alternator plug wire as well as troubleshooting a presistant 4.3 volts to the pink igniton feed wire that keyed the msd.