deisling question

[76bonanza]

I have had this truck for about 2 weeks and the last two days it has started on ocasion deisieling after I turn key off not real bad but enuf. Question I replaced the throtle return springs with lighter ones they seem to pull it back all the way and after it does it I check and the throttle is on the stop. Could it be when it is running it is not closing all the way sometimes then when it stops it does close? What are some other cuases of the run on? Bad gas?

[sneakysnake]

The two main reasons for dieseling are excessive carbon build up in the combustion chamber and timing.

[76bonanza]

Timing to high? Or to low? I dont think it is build up the motor only has about about 1000 miles on rebuild block and heads. It is wierd it only started about 2 days ago but it has been hot also. And almost imediatley after I changed the springs.

[sneakysnake]

Usually it needs to be advanced,Put a light on it. I dont know why a return spring would cause it to run on but you might try putting the old spring back on and see if it makes a difference, cant hurt.LOL

[76bonanza]

That is what I though but it ran fine for a week never did it, but the springs were really stiff put on some really soft springs to soft in my opion then it started and it does not do it ever time and not very bad. only thing I can think of is it my not be letting the butterfly close all the way? About what should the timing be I know that is an open ended question. Also I am almost sure the advance is on intake vaccum so it should be more advanced at idle?

[Longhorn Man]

A soft/weak spring could cause run on...but not likely.
Things to check;
timing being too far advanced
too low a grade of fuel
idle set too high
carboned up combustion chaimbers
valves not closing all the way
Poor work with sharp edges in the combustion chainber

[PICKMUP]

I am not sure what difference timing makes. When you turn off the key, the ignition should be off and I don't think the motor can tell where timing was with no fire.
These trucks are notorious for dieseling...BB & SB. The "anti-dieseling" solenoids worked well, because they let the butterflies close all the way, so there was no more air & fuel entering the intake.
Run the idle as low as possible and make sure the return spring is strong enough to pull the butterflies all the way down.
If all else fails...turn the engine off "in gear"...just don't forget to put it in park or gear when it stops.

[76bonanza]

Timing is set to about 12-13 at idle with vaccum plugged

[Longhorn Man]

Tried backing it back down to 8 or so? If it is a stock engine, that's what it's supposed to have.

[76bonanza]

It is not stock at all 355 roller rockers comp cam dyno about 330 hp 389 lbs build by hatfield racing in joplin mo not super bad but a little hot.

[Stocker]

Turn it off while still in gear.

[Alan Potter]

Idle is too fast

[masterbeavis]

Turning truck off while in gear still works, but how safe can that be? Especially if you forget to put it into park? All it takes is one time to forget. I vote for fix the problem, not learn to live with it.

[71400lb]

I had the same problem...turned out to be a combination of the idle too high and 87 octane gas...I've since switched to 93 octane and lowered the idle, and it hasn't diesled since March of this years!

71400LB

1971 Cheyenne 3/4 Ton Long Bed
400 SBC/400 Turbo
2wd

[fastwillie 696969]

back your timing down to 4 deg base timing
and pickmup you should read some hot rod mags about how timing does effect
shutting and overheating problem with timming

[acloco]

....and check the distributor to make sure the mechanical advance is not stuck/sticking/worn out..........

[fastwillie 696969]

http://www.streetrodstuff.com/Articl...ion/Page_2.php

[LUV2XCLR8]

Interesting Info

[jamal]

Originally Posted by PICKMUP

I am not sure what difference timing makes. When you turn off the key, the ignition should be off and I don't think the motor can tell where timing was with no fire.

The valves get too hot and light the mixture instead of spark, like glowpugs in a diesel, hence the name dieseling. Too lean, timing too far advanced, or high compression with low quality fuel. Try running better gas, but timing should do the trick.