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#2229177 - 04/11/11 02:57 PM What causes run-on and backfiring on shutdown?
deeter16317 Offline


Registered: 12/07/07
Posts: 1339
Loc: SE, PA
25HP Kohler Command runs-on ("diesels") and backfires upon hot shutdown, even if allowed to idle several minutes. It runs excellent otherwise...just got done mowing 2.5 acres of grass in under two hours and under a two gallons of fuel.

What's the fix? I want to remember this is a timing issue??
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#2229191 - 04/11/11 03:08 PM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
demarpaint Offline


Registered: 07/03/05
Posts: 20769
Loc: NY
It could be a timing issue or carbon deposits in the combustion chamber, or too fast an idle. Start off by checking the timing and idle speed.
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#2229192 - 04/11/11 03:09 PM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
Lethal1ty17 Offline


Registered: 07/01/10
Posts: 675
Loc: Georgia
i believe it is from fuel making it into the exhaust because it isnt combusted fully. i.e. its not atomized well by the carb or isnt allowed to burn fully from a bad spark. or it is just running lean and has excess fuel that keeps vaporizing. our 20HP kohler does the same thing if you dont let it idle for a minute.

ive also had a car do this too when i was seafoaming it. 2002 accord kept running even with the key out of the ignition.

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#2229196 - 04/11/11 03:14 PM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
deeter16317 Offline


Registered: 12/07/07
Posts: 1339
Loc: SE, PA
How would one remove carbon deposits?

It idles pretty low, lower than I actually like...but it idles.
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#2229200 - 04/11/11 03:15 PM Re: What causes run-on and backfiring on shutdown? [Re: Lethal1ty17]
deeter16317 Offline


Registered: 12/07/07
Posts: 1339
Loc: SE, PA
Originally Posted By: Lethal1ty17
i believe it is from fuel making it into the exhaust because it isnt combusted fully. i.e. its not atomized well by the carb or isnt allowed to burn fully from a bad spark. or it is just running lean and has excess fuel that keeps vaporizing. our 20HP kohler does the same thing if you dont let it idle for a minute.



It shouldn't be getting spark, the ignition is shut off!
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#2229207 - 04/11/11 03:29 PM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
2oldtommy Offline


Registered: 10/29/06
Posts: 834
Loc: Ohio
deeter, I would try some Regane or Techron in a tank of gas. Probably 1-2 oz. would be about right depending on the tank capacity.These work by turning the carbon to ash and blowing it out the exhaust. FWIW--Oldtommy

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#2229211 - 04/11/11 03:33 PM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
demarpaint Offline


Registered: 07/03/05
Posts: 20769
Loc: NY
Originally Posted By: deeter16317
How would one remove carbon deposits?

It idles pretty low, lower than I actually like...but it idles.



The cheapest way is to get a windex bottle filled with very hot water. Get the engine warmed up, idle the engine up to about mid rpm range and squirt the water into the carb while the engine is running. Squirt and increase rpms from mid range to 3/4 range. Don't go nuts squirting in water. Try about 6 ounces of water, as a spray mist, over a period of a few minutes.

You can also do a piston soak with Seafoam, or MMO. IMO if it is hard carbon the water mist I mentioned is the better option.
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#2229217 - 04/11/11 03:40 PM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
Lethal1ty17 Offline


Registered: 07/01/10
Posts: 675
Loc: Georgia
Originally Posted By: deeter16317
Originally Posted By: Lethal1ty17
i believe it is from fuel making it into the exhaust because it isnt combusted fully. i.e. its not atomized well by the carb or isnt allowed to burn fully from a bad spark. or it is just running lean and has excess fuel that keeps vaporizing. our 20HP kohler does the same thing if you dont let it idle for a minute.



It shouldn't be getting spark, the ignition is shut off!


i know, fuel can build up and ignite from hot bits inside of the engine even after the ignition is shut off.

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#2229233 - 04/11/11 03:56 PM Re: What causes run-on and backfiring on shutdown? [Re: Lethal1ty17]
JTK Offline


Registered: 08/14/03
Posts: 7176
Loc: Buffalo, NY
My 2005 model year Command 20 V-twin did the same thing. The solution per the owner's manual was to always have the engine throttled up upon shut-down. It feels unnatural to do so, but the fuel cut-off solenoid keeps any addition fuel from getting into the engine once you kill the ignition.

You don't have to be at max governed speed, just throttled up part way.

This is a common concern for lots of Command twin applications some do it, some don't.

Curiously enough, my Courage V-twin doesn't have this issue.

Joel


Edited by JTK (04/11/11 03:58 PM)
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#2229235 - 04/11/11 03:57 PM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
deeter16317 Offline


Registered: 12/07/07
Posts: 1339
Loc: SE, PA
OK, I'll try it...
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#2229296 - 04/11/11 04:52 PM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
660mag Offline


Registered: 12/29/10
Posts: 318
Loc: TEXAS
Could be an exhaust leak at your muffler gasket. Or your exhaust valve may not be seating well.
You can test for both of these issues with a cylinder leakdown tester.
Another place to look may be your fuel solenoid on the bottom of the carb. If it has one that is. When the key is turned off is should stop 100% of the fuel from entering the c chamber. That engine should be turned off ,according to Kohler. at WOT.

And yea carbon in the exhaust port would be another thing to look for. For removal water gets my vote.
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#2229313 - 04/11/11 05:12 PM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
660mag Offline


Registered: 12/29/10
Posts: 318
Loc: TEXAS
oops, looks like JTK just posted most of that.
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#2229379 - 04/11/11 06:16 PM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
JTK Offline


Registered: 08/14/03
Posts: 7176
Loc: Buffalo, NY
It's an aggravating thing for sure. I know my Command 20 would 'afterfire' so loud, it sounded like a shotgun going off. Scared the heck out of me the first time or two and I can't believe it didn't blow the exhaust system apart.

If shutting down at WOT is too bothersome, you can blip the throttle up after you kill the ignition. That works too. Anything to lean out that last bit of fuel vapor to the point it won't ignite.

Joel
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#2229794 - 04/12/11 07:14 AM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
deeter16317 Offline


Registered: 12/07/07
Posts: 1339
Loc: SE, PA
OK, shutting down under throttle doesn't bother me...it is completely the opposite of what I've always done. Typically shutting down under throttle (in the older engines) causes worse run on and backfiring!

How do you check the timing, or change the timing? I almost wonder if the timing isn't retard to far? The service manual only indicates checking for timing advance with the "SmartSpark" system. There is nothing about checking or setting timing.

I know it feels hotter than "normal", but its a completely different engine than I have used before so it might be normal for this breed of engine?

It runs like a scalded dog, even full tilt with fairly heavy grass (61" deck); it hardly changes tune.
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#2229812 - 04/12/11 07:47 AM Re: What causes run-on and backfiring on shutdown? [Re: deeter16317]
Nick R Offline


Registered: 07/14/09
Posts: 10424
Loc: Amherst, OH
I occasional get afterfire from the landmower with the brings, but more often the chonda powered snowblower, which does it more often than not.
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