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dgjks6

deiseling after stop

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dgjks6

Well, got the c-85 running perfect. Tried to mow a few times earlier, but kept getting stuckin all the mud. It was finally dry enough and I mowed. I learned a few things:

1 - 36 inch gives a great cut, but the grass can't be too long

2 - make sure you tighten the bolt that holds on the mule drive cover on or it will fall off and you will mow over it :hide:

Now for the question - when I turn it off, it keeps going. Any ideas on what to try? I heard in the pst this was caused by carbon build up in the exhuast port, but I know for a fact there is none there.

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rmaynard

Try using 93 octane in the next fill up.

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oldredrider

Adding a higher octane fuel does not FIX the problem. Most likely, the point gap is set incorrectly and should be checked. Point gap determines timing and it sounds like your timing is too far advanced, therefore causing dieseling.

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Horse'n Around

I don't know if the hot carbon is the source of your dieseling problem or not, but I really doubt that it is. However,if for some reason carbon is causing the problem, it wont be carbon in the exhaust port, It would be a buildup of carbon in the combustion chamber it self . In extreme cases, excess carbon in a combustion chamber can get hot spots that can get hot enough so that it can ignite the air/fuel mixture with or without a spark.

John

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rmaynard

Alcohol will vaporizes at a much lower temperature than the gasoline. Alcohol vapor in the combustion chamber can cause the engine to run on if you have any hot spots. Lower octane gas contains 10% alcohol. Many 93 octane gasolines don't. Therefore higher octane gas can help eliminate run on.

It's worth a try. :hide:

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VinsRJ

Deiseling is usually caused by improper timing issues.

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bitten

Let the motor cool down before shutting it off. I let it run at just above idle for a few minutes and then shut it down.

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MikesRJ

Assuming we're talking about a Kohler here, try this procedure for setting the point gap (engine timing) (Great little article written by our own T-Mo):

http://www.mywheelhorse.com/graphics/file/...ngineTiming.pdf

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Save Old Iron

skepticalbeaver2.jpg

With the ignition switch turned off so the coil has no primary voltage or the magneto is grounded,

how does timing come into play :hide:

look for another source of ignition of the fuel / air charge

check for carbon deposits or a glowing hot spots (sharp, thin edges) in the cylinder - damage to the edge of the piston crown, etc.

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oldredrider

Here is how timing comes into play: If the timing is too far advanced, the engine will run "hot"... i.e temperature. When an engine runs hot, the whole combustion chamber (especially carbon deposits) become a source of ignition. You don't need electricity to get fire in this scenario. After the primary source if ignition (spark plug) is switched off, whatever is left in the combustion chamber (carbon, etc.) can still fire the fuel, hence "dieseling".

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Save Old Iron

agreed

but raising the combustion chamber 50 - 100 - 150 degrees by a timing change would not cause dieseling without the presence of a small point source of heat far above the average cylinder temperature

a small, thermally isolated artifact in the combustion chamber is most likely the principle cause of the issue.

I would think complaints of the engine running "poorly" or power loss would be seen in addition to the dieseling complaint. But I'm going with the evidence presented in the opening statement of the post

"Well, got the c-85 running perfect".

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TT

a small, thermally isolated artifact in the combustion chamber is most likely the principle cause of the issue.

Perhaps like the ground electrode on the spark plug?

Let the motor cool down before shutting it off. I let it run at just above idle for a few minutes and then shut it down.

Great advice in any situation - dieseling or not. :hide:

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Save Old Iron

one more thought after I typed the "thermally isolated" statement,

possibly an overheated exhaust valve caused by poor contact with the valve guide. The valve stem can no longer transfer heat to the valve stem and then onto the block, so the valve stays hotter than usual.

a loose fitting exhaust valve - which may cause oil usage - which may get in the combustion chamber - then turn to the excess oil to coke - then the coke glows and .....

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dgjks6

got my work cut out for me tomorrow. the best part about the restoration I did is that now I actually understand what you guys are saying.

As far as running smooth, it starts easily and after choke closed it surges for about 10 seconds and then runs perfect at 3500 rpm's and will run all day long. However, it does give off more heat than my 312. I have only run 2 taks of gas through her so far, so I doubt anything can have built up so far.

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Gene_S

I'm having trouble with my diesel gasolining when I shut it off??? :hide:

Good compression and a hot engine can cause this dieseling. The engine still pulls fuel in after shutting the key off with no spark and heat and compression cause it to fire... Key word hot... Like Bitten said good point on letting the engine cool down at low idle for a minute or two will help. My 416-8 has all these symptoms and the timing is where it belongs...

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Save Old Iron

the best part about the restoration I did is that now I actually understand what you guys are saying.

and that sir is one of the best byproducts of this hobby - understanding !!

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