help with Dieseling - The 1947 - Present Chevrolet & GMC Truck Message Board Network

dmurphy68 · 07-21-2003, 05:59 AM

almost everytime i turn the truck off it diesels I have adjusted the carb and still does it. when it was cold out side it did not do it but now that it is summer it does it all the time.
specs
350 bored 30 over
rv cam
1405 carb (manual choke)
timming set at 8 deg btdc
running 89 gas

any thing you all can think of ?? also every now and then get a backfire up the carb. other than that it starts and runs good

thanks in advance
Darren

RipMeyer · 07-21-2003, 08:21 AM

Check the timing. I know you said you have it set at 8 deg but try a few different spots . Also make sure the idle is not to high.

dmurphy68 · 07-21-2003, 08:29 AM

idle is set at 900 and 600 in gear but I dont get it, it ran fine in the winter and colder months

Longhorn Man · 07-21-2003, 07:19 PM

Try running the 91 or what ever octain, see what it does.
The wife had an 84 K-car that would do this every time you shut it off, even if you left it in drive it would do it. An old man told me to try hi-test and bigger than shiznit, it worked.
Leaving it in gear when shutting it off should help, as does turning the steering wheel and depressing the service brake at the same time as shutting it off. (asuming you have both power steering and brakes)
How long has it been since the heads were off? If there is a possability of carbon deposits on the pison or combustion chaimber, you can SLOWLY pour a little dextron down the primarys with the engine running at 1500 RPM, a squirt bottle of watter injected the same way works too. (old school tricks to help pass emissions tests)Running a little lean can also cause this. Lean = hot spots, and all it needs is one point to be hot enough to ignite the unburned incoming charge as you kill the ignition.
Backing off the timing helps, but I doubt that is your problem here.
What does it idle at? An excesively high idle speed can also do this, but again, I doubt this is the issue either.

*67Fleetsidedream* · 07-21-2003, 07:33 PM

Start using 90+ octane and it will go away.
How many miles are on this engine?

oldtrucknut · 07-21-2003, 07:34 PM

It's probably the timing. try advancing it some more. My 400 small block is set well above 8 and it runs good. Also check to see if you plug wires are in proper sequence. good luck!

cableguy0 · 07-21-2003, 07:47 PM

i think his issue is heat the fuel is still combusting without spark. i agree try a higher octane in the summer months and see what happens

Longhorn Man · 07-21-2003, 07:52 PM

advancing the timing would more likely than not make matters worse. With more timing comes more heat, and heat is the main thing that causes dieseling.

dmurphy68 · 07-21-2003, 09:00 PM

it only has 2500 miles just rebuilt in winter I am running 89 in it but will try a tank of high test donty want to but got to pay the $$

sbc350gearhead · 07-21-2003, 09:46 PM

Try a combustion chamber cleaner (or one of longhorn's tricks), or richen the mixture a hair. If that doesn't work, then try a colder plug.

07-21-2003, 05:59 AM	#1
dmurphy68 Registered User Join Date: Nov 2002 Location: Middletown ohio Posts: 1,058	help with Dieseling almost everytime i turn the truck off it diesels I have adjusted the carb and still does it. when it was cold out side it did not do it but now that it is summer it does it all the time. specs 350 bored 30 over rv cam 1405 carb (manual choke) timming set at 8 deg btdc running 89 gas any thing you all can think of ?? also every now and then get a backfire up the carb. other than that it starts and runs good thanks in advance Darren __________________ The very atmosphere of firearms everywhere restrains evil interference. When firearms go, all goes, we need them every hour. - George Washington No free man shall be debarred the use of arms - Thomas Jefferson Later Darren http://www.myspace.com/dmurphy68 Last edited by dmurphy68; 07-21-2003 at 06:01 AM.

07-21-2003, 08:29 AM	#3
dmurphy68 Registered User Join Date: Nov 2002 Location: Middletown ohio Posts: 1,058	idle is set at 900 and 600 in gear but I dont get it, it ran fine in the winter and colder months __________________ The very atmosphere of firearms everywhere restrains evil interference. When firearms go, all goes, we need them every hour. - George Washington No free man shall be debarred the use of arms - Thomas Jefferson Later Darren http://www.myspace.com/dmurphy68

07-21-2003, 07:34 PM	#6
oldtrucknut 67-72 truck surgeon Join Date: Jul 2003 Location: Indiana Posts: 155	It's probably the timing. try advancing it some more. My 400 small block is set well above 8 and it runs good. Also check to see if you plug wires are in proper sequence. good luck! __________________ 1969 Chevy C10 1993 Toyota Camry LE 1999 Ford F250 Super Duty 4x4 diesel 2008 Dodge Charger Super Bee 1953 International R182

07-21-2003, 07:47 PM	#7
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	i think his issue is heat the fuel is still combusting without spark. i agree try a higher octane in the summer months and see what happens __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

07-21-2003, 09:00 PM	#9
dmurphy68 Registered User Join Date: Nov 2002 Location: Middletown ohio Posts: 1,058	it only has 2500 miles just rebuilt in winter I am running 89 in it but will try a tank of high test donty want to but got to pay the $$ __________________ The very atmosphere of firearms everywhere restrains evil interference. When firearms go, all goes, we need them every hour. - George Washington No free man shall be debarred the use of arms - Thomas Jefferson Later Darren http://www.myspace.com/dmurphy68 Last edited by dmurphy68; 07-21-2003 at 09:02 PM.

07-21-2003, 08:21 AM	#2
RipMeyer Registered User Join Date: Oct 2001 Location: Southern New Mexico Posts: 649	Check the timing. I know you said you have it set at 8 deg but try a few different spots . Also make sure the idle is not to high.

07-21-2003, 07:19 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Try running the 91 or what ever octain, see what it does. The wife had an 84 K-car that would do this every time you shut it off, even if you left it in drive it would do it. An old man told me to try hi-test and bigger than shiznit, it worked. Leaving it in gear when shutting it off should help, as does turning the steering wheel and depressing the service brake at the same time as shutting it off. (asuming you have both power steering and brakes) How long has it been since the heads were off? If there is a possability of carbon deposits on the pison or combustion chaimber, you can SLOWLY pour a little dextron down the primarys with the engine running at 1500 RPM, a squirt bottle of watter injected the same way works too. (old school tricks to help pass emissions tests)Running a little lean can also cause this. Lean = hot spots, and all it needs is one point to be hot enough to ignite the unburned incoming charge as you kill the ignition. Backing off the timing helps, but I doubt that is your problem here. What does it idle at? An excesively high idle speed can also do this, but again, I doubt this is the issue either.

07-21-2003, 07:33 PM	#5
67Fleetsidedream Wiseass secured himself a BAN Join Date: Nov 2000 Location: MOON!!! Posts: 2,282	Start using 90+ octane and it will go away. How many miles are on this engine?

07-21-2003, 07:52 PM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	advancing the timing would more likely than not make matters worse. With more timing comes more heat, and heat is the main thing that causes dieseling.

07-21-2003, 09:46 PM	#10
sbc350gearhead Registered User Join Date: Mar 2003 Location: Columbus Ohio Posts: 1,413	Try a combustion chamber cleaner (or one of longhorn's tricks), or richen the mixture a hair. If that doesn't work, then try a colder plug.

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