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gas engine desieling

A

Anonymous-0

Well-known Member

have hariss 44 and a d17 allis they both try to run after being shutt off. dut new plugs, wires and pionts in. they both start very well and run threw the rpm range well.
 
Make sure your idle is clear down before shutting off.

Remember, once you shut off, there is no electrical.

Allan
 
How long since the head was off to decarbonize?? Uncles WD45 had dieseling- pulled head and found about 1/2 cup of carbon in each cylinder. Cleaned and reinstall, no dieseling, run smooth ut seemed a bit less power- in affect the carbon acted like a high compression piston during work runs and the deiseling was from the hot edge of carbon coat igniting fuel mix after sparks from spark plug stopped. How is oil comsumption? a cup of oil a week getting by rings and valves means some unburned carbon build up inside cylinders. Some carb cleane pour down carb throat at fast idle or just some water vapor may help loosen some of the carbon- otherwise pull head and scrape. A fiber optic probe inside the spark plug hole can show carbon build up without removeing head. Valve lip margin is another possible hot spot source- and combined with carbon build up on valve face can be cause of dieseling. Old tractor shutoff drill was simple turn off the gas tank petcock and let engine idle down a couple minutes as it ran out of fuel, no dieseling without some gas vapor in cylinder. The final lean mix would also take out a little bit of unburned carbon. Extra hot head from coolant crud is a third source- temperature guage read in red zone moost of time? RN
 
Set the idle to factory specs and reduce engine speed to idle before shutting off the ignition.

Dean
 
Could pull the plugs, fill each cylinder with Siloo, let it set over night. Next morning pull plugs, diesel engine over to remove Siloo.Re install plugs,and start,run at idle for a while, drain and change oil.Should remove the carbon from the cyl head,Worked on old straight six car engine.
LOU
 
You say "Well for once no one said check ignition timeing!" You say that because with the ignition off, timing cant have anything to do with dieseling right ?
I always thought the same thing until about a year ago. With no spark, how can timing have anything at all to do with an engine's tendency to diesel ???

Well i found out last year that ignition timing can have everything to do with an engines tendency to diesel at shutdown.

I have a heavy tandem truck with a GMC 478 V6 engine. As long as I have owned this truck, it ran hot, was underpowered and dieseled terribly at warm shutdown.
Last year I discovered the timing marks on this engine had slipped position(damper outer ring had slipped) and actually were running the timing very late, very retarded.
I repaired the timing marks and correctly timed the engine. It now ran much cooler and had much more power. Another thing really shocked me, this old engine no longer dieseled at a warm shutdown ????? Why ??? The late ignition timing was making the exhaust valves run very hot, hot enough to light off the fuel and keep the engine rattling along on a few cylinders.

So I learned that late ignition timing can have a dramatic effect on an engines tendency to diesel at shutdown. Your never too old to learn new things ;-) Im 64. ;-)
 
Very good point about ign timing. It does affect dieseling upon shutoff. Not from the spark as there is none but just exactly like you explained. Hot spots made hotter by improper timing.
 

And how much carb. tweeking did you do to get back some power/smooth out the engine before finding the harmonic ballancer had slipped? I'm surprised the engine even ran with timeing far off enough to run that hot.If a timeing light is not handy or timeing marks are unreliable a vacume gauge can get you really close on timeing along with a good ear.
 
(quoted from post at 16:44:47 05/20/13) You say "Well for once no one said check ignition timeing!" You say that because with the ignition off, timing cant have anything to do with dieseling right ?
I always thought the same thing until about a year ago. With no spark, how can timing have anything at all to do with an engine's tendency to diesel ???

Well i found out last year that ignition timing can have everything to do with an engines tendency to diesel at shutdown.

I have a heavy tandem truck with a GMC 478 V6 engine. As long as I have owned this truck, it ran hot, was underpowered and dieseled terribly at warm shutdown.
Last year I discovered the timing marks on this engine had slipped position(damper outer ring had slipped) and actually were running the timing very late, very retarded.
I repaired the timing marks and correctly timed the engine. It now ran much cooler and had much more power. Another thing really shocked me, this old engine no longer dieseled at a warm shutdown ????? Why ??? The late ignition timing was making the exhaust valves run very hot, hot enough to light off the fuel and keep the engine rattling along on a few cylinders.

So I learned that late ignition timing can have a dramatic effect on an engines tendency to diesel at shutdown. Your never too old to learn new things ;-) Im 64. ;-)
Click to expand...

Thanks Jon! I knew from many instances over the years that too much timing would cause dieseling, but don't recall that explanation.
 
If you have points and condenser ,, Along with what others are saying ,,, Change it over to ELETRONIC IGNITION ,, Oriellys stocks it for all cantankerous gasers
 
The owners manual for my mower suggests turning off the ignition, and at the same time, opening the throttle wide open to prevent run-on. It works so good that I do the same now with my old John Deere tractor.
 
Run the engines hard with a coolant temp of a minimum of 180F and 195f is better. Lean the idle not for smoothest idle but as lean as it will idle without actually missing. Lean the main jet for minimum fuel for smooth operation, instead of rich for max power.
Use a low ash engine oil rated for post 2007 diesel pickups.
As previously stated, the engines are crapped up with soot from putting around cold and rich.
High octane fuel isn"t going to break the budget either.
 
The only carb tweeking was to reduce the idle speed back to normal after advancing the timing.
The truck has an Allison automatic transmission, so the idle rpm needs to stay right at the stock rpm spec to avoid hard shifting into gear..
 
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