496 dieseling when shut off - Team Camaro Tech
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post #1 of 10 (permalink) Old Apr 19th, 15, 06:31 AM Thread Starter
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Exclamation 496 dieseling when shut off

I just read 100 threads on dieseling and I feel I have everything adjusted and 496 still diesels at shut off. The timing is set at 13-14 initial with 39-40 total and no vacuum advance on MSD distributor. I have the car idling at 800 rpms. This is the first time ever using a speed demon carb, it's an 850cfm. Idle screw are 1.25 turns out. Not sure on the secondary side how far the blades are open. I read there is also a idle screw in center of carb under air cleaner stud is.

What should I check now to get dieseling to stop. The 496 has large solid roller as well.

Thanks, Erik

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post #2 of 10 (permalink) Old Apr 19th, 15, 08:07 AM
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Re: 496 dieseling when shut off

What is the compression of the engine ??? Are you using Premium gas 93 octane or better ?

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post #3 of 10 (permalink) Old Apr 19th, 15, 12:38 PM
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Re: 496 dieseling when shut off

Could be a vacuum leak somewhere
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post #4 of 10 (permalink) Old Apr 19th, 15, 04:51 PM
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Re: 496 dieseling when shut off

Mostly it is octane & idle speed related.

The higher your idle speed, the less the engine is choked off & the higher tendency to want to run on.

Typically is can be overcome with higher octane fuel.

You ignition timing settings has nothing to do with it, as once you turn the key off there is no spark.

Assuming you mean your vacuum advance is not connected, but present... You may be able to hook up the vacuum advance to manifold vacuum. This will make the engine want to idle faster due to the additional timing at idle. Correspondingly you can then back out the idle speed screw to get the idle back to your original setting. This will help to choke off the engine when you turn it off.
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post #5 of 10 (permalink) Old Apr 19th, 15, 05:24 PM Thread Starter
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No vacuum advance on distributor. MSD billet ready to run. This is a 9.8.1 motor by what previous onwer stated. took carb off today and reset it to factory specs. The front and rear butterflies needed to be set the same and they weren't but they are now.

I am running 93 in it. I will bump timing back up to 14-16 and play with carb some. I assumed with the higher timing the idle screws would not have to be out as much. Also the float bowls were at there highest setting so I lowered them as well.

Thanks, Erik
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post #6 of 10 (permalink) Old Apr 19th, 15, 05:39 PM
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Re: 496 dieseling when shut off

Erik
Do you have a MSD ignition box ?

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post #7 of 10 (permalink) Old Apr 19th, 15, 06:00 PM Thread Starter
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Yes, 6AL box and msd coil
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post #8 of 10 (permalink) Old Apr 19th, 15, 06:25 PM
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Re: 496 dieseling when shut off

https://www.msdignition.com/WorkArea...id=15032386116
Go to page 8
Maybe this will help...

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post #9 of 10 (permalink) Old Apr 19th, 15, 07:17 PM
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Re: 496 dieseling when shut off

If the engine can withstand more initial timing, it should help the situation.

Just be sure adjust the centrifugal advance to keep the total from getting too high.
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post #10 of 10 (permalink) Old Apr 19th, 15, 08:38 PM
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Re: 496 dieseling when shut off

Quote:
Originally Posted by Erik Beckett View Post
Yes, 6AL box and msd coil
Did you go through the detailed setup directions ?

http://www.demoncarbs.com/Assets/doc.../LIT350rev.pdf

I noticed this comment :

Due to the choke horn's increased airflow design, and dependent on what air
cleaner/air cleaner gasket combination is used, a slight dimple in the air cleaner
may be necessary to allow for the butterfly to have a complete range of motion.
Failure to do so could result in a vehicle with an increased idle that could make the
vehicle hard to stop or control.

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