Kohler dieseling at shutdown

[ScottInCabot]

I've already called a talked to a tech(sorry, forgot the fellas name).

My newly purchased WMLT28 w/Kohler 19hp has a 'farting problem'(hey, that's what my wife calls it).  I allow the engine to idle to the lowest rpm and when I turn the key off, she will backfire every time...or worse, it engine diesels.

The tech asked if what type fuel I used.  I informed him unleaded 91 octane(non-ethanol).  He said that was 'good'.
The tech asked if the engine was idled all the way down.  I informed him that it was.  He said that was 'good'.

I questioned him to whether anyone else has had issues. He stated only if ethanol type fuels were used or the idle was to high when the key was turned off.



So....what now?  I'm not a small engine mechanic, and I don't want to be one.  I do not mind changing oil or fuel filters, cleaning air filters(or replacing as needed), and making sure 'things are tight and in functioning condition'.  This motor has approximately 22hrs, and I think it shouldn't have this problem....


What needs to be done to fix it?  Please....advise.






Scott in Cabot

[starmac]

I have to wonder if the low idle is not set right. It is always timing or fuel, and I doubt it has any timing adjustment on that engine.

[hamish]

What model and spec is your engine?

Most likely your engine is equipped with a anti-after fire/fuel stop solenoid.  Look for a long cylindrical housing securing the fuel bowl onto the carb.  If so you need to shut the engine off at when the throttle is at 1/2 to full throttle.

[bkaimwood]

Most popular causes of symptoms listed are...
1-idle speed set to high
2-fuel shutoff solenoid not functioning properly
3-higher than normal engine or combustion chamber temps...typically caused by excessive carbon build up, poor engine cooling, or lean fuel mixture...in your case, the first 2 causes of high temp most likely don't apply
4-improper ignition timing
-note that carbon in cylinders absorbs fuel, and stays hot once heated, sitting there like a hot coal...so when you turn the key off, the spark plug stops sparking, but the engine tries to continue running on this auxiliary fire source...overall high engine temps can do the same...lean fuel mixtures also can have the same impacts, increasing combustion chamber temps...just sayin'...good luck!!

[submarinesailor]

We had the same problem until we started allowing the motor to cool down for several minutes after cutting.  We believe that the motor gets quite hot while the motor is pulling thru a cut.  So after finishing a log or large cut, we let it idle for several minutes before we turn it off: for the next log, a break or the end of the day.  This has helped a lot.  We get very little popping/backfiring/farting from the motor when we do this.

Bruce

[snowshoveler]

At the service schools, Kohler has been all over the map on this sort of thing.
The muffler is still very hot when you shut off the engine and as it coasts to a stop its still pumping fuel through the engine.
When the right mix builds up in the muffler ...ka blooie. Some engines will just about scare the crap out of you when this happens.
Best results for most but not all folks is to bring the engine down to half throttle for a minute or so before shutting it off.
Remember these are a fan cooled motor and the fan has to be going fast enough to do its job.
A lot of new engines don't even have an idle circuit or control on them.
Regards Chris

[tyb525]

I've had the same problem with a 20 horse lawnmower engine. It will always backfire if you shut it off too soon. If I let it idle for a couples minutes, no backfire.

[sawguy21]

snowshoveler has it. You are getting an after fire, as the engine spools down with no spark the ignition has been shut off, raw fuel/air mix is sucked through and meets up with a hot muffler. Back fire through the carburetor is a whole 'nother problem usually related to ignition issues.

[bkaimwood]

The last few posts have good information...but a few things are still concerning. A muffler that running too hot and igniting fuel after shutdown certainly would explain the backfire concern. But would likely not explain the run on/dieseling, if, in fact, that's also going on. If the exhaust system is hot enough to act as an ignition system, and causes this, in my opinion, there is still a problem, or at the least, a design flaw. Other fellas have said that allowing the engine to idle for a brief period before shutting it down prevents it. That's good that there's a "fix", but not really. If I had spent that kind of money on a mill, and was told I had to allow cooldown idle for a while before shutdown, I wouldn't like that answer. The muffler ignition may be the cause of the ignition, but not the root problem. This support one of the things I listed earlier, engine running too hot, and supporting ignition after the engine is shut down. Why? I am kind of leaning toward the lean fuel mixture under these circumstances. Mostly because its a newer, low hour engine. As mentioned, many of newer engines, no matter who made them, are a hair lean, due to emissions. This makes everything run warmer than it would if the mixture was right, or a hair richer. When my exmark kohler engine runs on in the heat of the summer, it a sign that, well, its hot... idling for a brief moment does prevent it. But its not the fix or the cause. It tells me its time to clean and adjust the carb, cause its lean, if the idle speed is ok. I clean and adjust the carb, and its good for another 2 years. One may think that richening the fuel mixture may cause this, or make it worse, due to the extra fuel. This is not so... remember where the fuel is at, and how much is not the problem in this scenario, its where the source of ignition is coming from. If this is the case, I would check and/or adjust the fuel mixture to manufacturer specs...if the screws are where they are supposed to be, I would pull and check the spark plug color. Then richen the mixture slowly, run the engine under normal operating conditions, and recheck the plug. Keep doing this until the plug has the right color on it.

[47sawdust]

My Craftsman mower has a 14hp Kohler.It will backfire every time I shut it off with the key.If I let it idle down,pull out the choke,and turn the key it never backfires.

[millwright]

I installed a tiny tach on my 25 , the idle was too high from factory. A simple adjustment took care of the problem

[ScottInCabot]

Thanks everyone for your inputs.

> I usually allow quite a bit of time to allow the engine to 'sit and idle'....not sure what amount of time has passed, but it's usually 30-45 seconds.  If waiting longer will help, I can find something more to do while waiting...
> Hot exhaust...I can see that causing an issue.  Not sure how to overcome that problem, even idling for a 'while' will still keep hot gases in it.  Would a larger exhaust cure the issue?
> Dieseling......that isn't an issue of fuel in the exhaust.  And the occurrences, while not written down at time of incident, 'seem' to be getting closer together(this is just my observations from running the mill-happens once during one job, twice during next, four times during the latest job.....) and I would only guess(again, I'm not a small engine mechanic) that this doesn't help increase the life of an engine.
----How do I get this issue fixed?



And how many other WM LT28 w/19horse operators are having this occur?




Scott in Cabot

[Ox]

How about turning the gas valve off while running and let the engine suck the carburetor bowl dry?  No fuel, no ignition, no "farting".  It's good to this for winter storage anyway.  I'm sure you'll be able to time it just right after a few tries and get it to the point that you can plan ahead of time and have it running out of gas very soon after your last cut.

[Don_Papenburg]

But killing a hot engine is still not a good thing , I would let it idle for a minute or so then shut down the fuel .   That should be done by the fuel solenoid on the carb. check that for proper operation.

[LeeB]

This is not a new problem with Kohlers. The 15 hp Kohler I had on my TK 1200 14 or 15 years ago did the same thing.

[drobertson]

This is not a new problem with Kohlers. The 15 hp Kohler I had on my TK 1200 14 or 15 years ago did the same thing.

I was going to say the same,, I had a 19.5 hp, mower, did the same, at times, letting it cool down helped.  I have a Briggs 6.5 on the tiller, maybe 10 years old, or more, it does it too, idling down and letting it run for a spell help.  I still hate to hear it or have to wait.  It should be addressed, just not sure how to go about it.

[tyb525]

I have heard/read from various sources that letting any engine idle for a minute or two before shutdown is better for it, especially after running it hard. A good design shouldn't backfire or afterfire after shutdown though, as long as you didn't cut the ignition at full rpms.

[Kbeitz]

It's new engine design problems. I collect old garden tractors. I would always run the engine halt throttle or less to do my work. Try that with the new stuff and you have problems. Newer tractors the engine is really closed in and don't have room to breath. The newer engines need to run wide open to keep somewhat cool.
To meet the stiffer smog laws they lean out the gas and take away the carb adjustment.
Most of the time there is no fix.

[Dave Shepard]

Cool down is a good idea with any engine. It has nothing to do with his much one paid for their mill. If you don't cool down a hot turbo diesel, you will eventually have bigger problems than backfiring. It's just part of good machinery operating.

[ScottInCabot]

OX.....while I'd love to 'store' the mill for winter, oh wait....we don't really have much of a winter in central Arkansas!  Few days below freezing, maybe a few flurries(up to about 3" at most-and it melts the next day or two)....  I'll be milling through the winter....it's easier on me not doing a lot of milling in the summer anyway ;)

Dave Shepard......'turbo diesel'?  This is a gas motor....



I can live with the 'farting'....it's the dieseling that has me more concerned about engine life.

Scott in Cabot

[Verticaltrx]

I have an LT15 with the new 19hp Kohler and it has on occasion dieseled. The fix is to let the motor cool down properly before shutting it off. 30-40 seconds isn't enough, I let mine idle/cool down a good minute or two (sometimes more if I've really been pulling it hard) and haven't had any dieseling or backfires since.


As others have stated, this should be common operating practice for any equipment.

[tnsnakebite]

Perfect.

[Dave Shepard]

OX.....while I'd love to 'store' the mill for winter, oh wait....we don't really have much of a winter in central Arkansas!  Few days below freezing, maybe a few flurries(up to about 3" at most-and it melts the next day or two)....  I'll be milling through the winter....it's easier on me not doing a lot of milling in the summer anyway ;)

Dave Shepard......'turbo diesel'?  This is a gas motor....



I can live with the 'farting'....it's the dieseling that has me more concerned about engine life.

Scott in Cabot

My point was that idling an engine down is just part of the process of running equipment. Just because someone bought a new mill doesn't obviate the need for proper operation, as bkaimwood seemed to be suggesting.

[ScottInCabot]

OX.....while I'd love to 'store' the mill for winter, oh wait....we don't really have much of a winter in central Arkansas!  Few days below freezing, maybe a few flurries(up to about 3" at most-and it melts the next day or two)....  I'll be milling through the winter....it's easier on me not doing a lot of milling in the summer anyway ;)

Dave Shepard......'turbo diesel'?  This is a gas motor....



I can live with the 'farting'....it's the dieseling that has me more concerned about engine life.

Scott in Cabot

My point was that idling an engine down is just part of the process of running equipment. Just because someone bought a new mill doesn't obviate the need for proper operation, as bkaimwood seemed to be suggesting.

And once again...."turbo diesel"?
But I guess you're too busy 'attacking me'???  Wow!

Please block me or ignore me there Dave, I'm not in the mood for your drama.....




Scott in Cabot

[LeeB]

I don't think anyone was attacking you Scott. The man was simply saying that any engine including turbo diesels need to cool down before killing them. A turbo won't backfire if you don't cool it down but will soon enough suffer the consequences the same as a gas engine would.  Attacks around here are few and far between. This is just not that kind of forum.