dieseling big block - Team Camaro Tech
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post #1 of 9 (permalink) Old Nov 5th, 05, 03:25 PM Thread Starter
 
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dieseling big block

To all, I have a new 434 big block. Comp Cam, Holley Carb (mild street), Headers, 4 speed, MSD dist and Ig.
I am setting the initial timing at 8 with a 28 degree bushing in the dist. When shutting down, the motor wants to stay runnning (dieseling). I have tried several combos but still happening.
The motor runs very well while driving. The temp stays around 182.
I've checked the dist with a high tech light and the total timing is 36 at about 2800 rpm. The idle is set at 850 and the response is very good. The carb is a street avenger.
Does anyone have any suggestions. The last one I got was 'Octane'. I just put 104 octane boost in and will try again tomorrow.
HELP!

Jim Whittaker
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post #2 of 9 (permalink) Old Nov 5th, 05, 04:11 PM
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Steve
 
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Re: dieseling big block

Low octane is a reason for dieseling.. Otherwise, your plugs heat range could be too high, or you may have a large build up of carbon deposits that could cause it too.

Your timing and idle speed sound reasonable.

Nov 68 Van Nuys. 327 floor-shift-auto, Frost Green and not much else when new.

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post #3 of 9 (permalink) Old Nov 5th, 05, 09:45 PM Thread Starter
 
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Re: dieseling big block

I hope your name is Steve. The low octane comment is the second time that I heard that. I am working on that with an octane boost. I added it today. No one has said anything about plugs. How should I order a 'heat range' for the plugs. I have to look at one tomorrow and read the number on the plug. I'll let you know. As far as carbon deposits, the motor has about 10 hours of running and maybe 15 miles. It is really brand new. I'll check the plugs and see how the octane boost alters things. Thanks for the reply.

Jim
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post #4 of 9 (permalink) Old Nov 5th, 05, 10:19 PM
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Re: dieseling big block

Jim,

Some other common causes of dieseling are too much throttle opening or too high of an idle. I would try raising the initial timing to 14-16 degrees which would allow you to lower the throttle blade opening.

Also 104 octane boost will do little to raise octane. Try the timing or lowering the idle speed if possible.

Jody


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post #5 of 9 (permalink) Old Nov 5th, 05, 11:35 PM
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Re: dieseling big block

Yes my name is Steve!
If your plugs are too hot, you will be able to tell from very white and blistered porcelain.. Basically if the heat range is too hot, they wont be able to disapate heat and can glow, acting like a glow plug.
The same thing happens with heavy carbon deposits, but you say this is a new engine so I doubt that one.

I think your best sorting your timing and throttle position as suggested with a good fuel.

Nov 68 Van Nuys. 327 floor-shift-auto, Frost Green and not much else when new.

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post #6 of 9 (permalink) Old Nov 6th, 05, 12:03 PM
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Re: dieseling big block

Messing with the timing won't do anything,..once the key is off, there's no more spark to the plugs. Try:

1) Reducing idle speed.
2) Leaning the idle mixture
3) Cooler plug (I use Autolite 3924's on Alum heads,..you might try 24's on iron heads,..unless you use the big plug,..don't know the number. 26's and 3926's are hotter).

If she still diesels, jet her down a notch or two.

Just a guess, but I'll bet you run 10-11 compression or more. Higher compression aggravates the problem.

Of course, you can always leave her in gear when turning off the motor or let the clutch out slightly.

Good luck!
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post #7 of 9 (permalink) Old Nov 6th, 05, 01:21 PM
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Re: dieseling big block

Advancing the initial timing does help sometimes because it allows you to turn the idle down to the point where you're actually using the idle circuit.
From my experience leaning the idle or the primaries only makes things worse. Ever work on one of those late seventies lean burn engines? They were notorious for valve ping and dieseling.
With higher compression you normally have to jet UP not DOWN.
A cooler plug or a plug with a shorter reach on the electrode might help. By that I mean a tip that doesn't extend into the combustion chamber as far.

69 RS 355 Tremec 5-Speed 4.11's
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post #8 of 9 (permalink) Old Nov 6th, 05, 05:46 PM
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Re: dieseling big block

I'd agree with Jody and 12run. Bump your initial up to 14, or even 18. Put the black bushing in the distributor, and get the throttles closed more at idle.





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post #9 of 9 (permalink) Old Nov 6th, 05, 07:47 PM Thread Starter
 
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Re: dieseling big block

Thanks to all of you for the suggestions. I picked up some cooler plugs today but will definitely pick up the 3924's that were suggested tonight. I will try to timing advance and throttle closing suggestion tomorrow. Will keep you all posted.
THanks,
Jim
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