Diagnose Kohler engine problem...

Discussion in 'Lawn Mowing' started by Bassman, Mar 1, 2001.

  1. Bassman

    Bassman LawnSite Senior Member
    Messages: 270

    I have an Exmark Lazer Z w/ 25H.P. Kohler Command vertical crankshaft engine. It has been a very reliable mower. I have app. 1400 hrs on engine. Several months ago, I noticed that very infrequently, the engine would start to bog down momentarily-this only happens about 5% of the time. Usually it happens when it's shut down hot and sometimes commences when I first power it up again after shutting down for a short time. It's like it isn't firing on both cylinders, sort of like it's not getting enough gas and a small amount of black smoke comes out of exhaust. After about 20 seconds or so it begins to gain R.P.M.'s and runs great, black smoke disapears. Like I said, this happens very infrequently but I wonder what is causing it. It does NOT burn any oil. I took it in to the dealer and he replaced plugs, etc. It still does it. I guess I don't blame him, it's one of those things like with a car or truck, if it does not run poorly 95% of the time and the dealer does not notice any thing wrong, he figures everything is o.k. Could this be a carburator adjustment/fuel mixture problem? Or head gasket problem? I just don't want to ignore it and something major happen. Any thoughts would be appreciated.
    P.S. I'll take it back to dealer when I get thge time, I'm hoping some of you guys can give me some idea to tell the dealer to check.
  2. guntruck

    guntruck LawnSite Senior Member
    Messages: 527

    I would tend to lean more towards the carb end of the scenario. It doesnt sound like an adjustment though due to the fact that it does it so infrequently. And assuming that you have changed the fuel filter and checked the carb for lodged debris i would stand on the air/fuel mixture. I am no certified mechanic but a desent back yard one and this is my opinion.
  3. Runner

    Runner LawnSite Fanatic
    Messages: 13,497

    When you shut it down, you have to let it idle down for about 30 seconds or so first. This allows the fuel in the bowl to go back down and allows the float to settle. What's happening, basically, is that your engine is entering the beginning stages of flooding out. That's the black smoke you see when it is first fired up again. The sputtering or hesitation is from too much fuel in the cylinder(s) as well. Does it backfire on you when you go to restart it? This is not that uncommon when it is not allowed to idle down too. What I do, as a time saver, is when I put it up on the trailer, I brake it, get off the machine, and put the gate up while it is idling. Then, I just reach up to shut the machine off. This idling time is then better utilized and not wasted just sitting there waiting for it to idle for the needed time. Try it and see, and I think you will find that this will probably take care of your problem.
  4. Jerrys Lawn Service

    Jerrys Lawn Service LawnSite Member
    Messages: 155

    Bassman,check with a new member, Gorfis he says he's been a small engine man for 7 years and would be glad to try to help with any questions.

    Good Luck!
  5. GreenQuest Lawn

    GreenQuest Lawn LawnSite Senior Member
    Messages: 822

    Try to replace the hydro filter (if you havent already). Mine did the exact same thing only i noticed when i went up hills with the blades on. Replaced everything else first but ended up being the hydro filter. (and it was only 150 hrs since last filter change) so i have started changing it more often.
  6. captdevo

    captdevo LawnSite Senior Member
    Messages: 932

    it sounds like it may be loading up, getting to much fuel. You should have the carb rebuilt, and ask them to check for wear on all orfices (from additives and cleaners). If this does not resolve the problem, do a compression test with leak down, you may have a worn valve or be spinning a ring.
  7. Jman

    Jman LawnSite Member
    Messages: 217

    It sounds to me like you are getting a vapor lock problem in the carb while it sits for a short time while hot. Poorer quality fuels we have to use now a days contribute to that. Also I have a suggestion for shut down. You guys are using air cooled engines, they get their air from the fan pulling into the engine that is located on the flywheel. The slower you Run the engine the less cooling air you get to it. My suggestion is to run it wide open, NO load. The throttle plates on the carb are not open and you get all the rpm needed to keep the fan going at speed. Also on the Kohler engines they need to be shut off at half throttle or higher. They have a fuel shutoff solenoid in the high speed circuit of the carb. If you shut them off at idle you still pull fuel in to the engine fromthe idle circuit and you can end up with brown seat sindrym when you start climbing off (after bang). I shut my Kohler units off at wide open throttle. They are constantly getting oil from the oil pump and lubricating all surfaces and no fuel is getting into the engine to wash the cylinders down. These are just my opinions.
  8. Bassman

    Bassman LawnSite Senior Member
    Messages: 270

    Thanks for the replies. From the posts so far I think I'll either let it idle for a few moments before shutting down and/or also try shutting down with throttle at high end. If this does not stop it, I'll try replacing the hydro-filter.
    As I stated, the overall performance is fine. I just notice this when it's hot and I've shut down and then restarted a short time later. I have always idled down after mowing and then immediately shut down, like right away. No biggie, mower runs great once I'm powered up. Thanks for info so far. More replies appreciated.
    P.S. My engine has sometimes diesels just a tad when quiting and often when it does not diesel it shuts down with a pretty good backfire. Is this normal?

    [Edited by Bassman on 03-02-2001 at 04:03 AM]
  9. Runner

    Runner LawnSite Fanatic
    Messages: 13,497

    No, a backfire is NOT normal. Sooner or later, you are liable to blow your exhaust off. I have done that before. Just let it idle down a bit(give it a good chance-atleast 30 seconds or so) and then shut it off. I will bet a dollar to a donut this will cure your problem. As a matter of fact, PLEASE let us know how it turns out. Remember this thread, and post on it. It will come back to the top. :)
  10. John DiMartino

    John DiMartino LawnSite Silver Member
    Messages: 2,555

    There is nothing wrong with letting your 25 idle for 30 seconds before you shut it off.The fan may turn slower at idle-but the engine isnt generating hardly any heat either with no load,and idle speed,friction is low,as is fuel usage which keeps combustion temps down,and My 25 is not a Command pro-the pro is the only one with the fuel shutoff-if you dont have a pro-you should be idling down before shutting it off.If you dont and let it wind out,the exhaust is hot at wide open,you shut if off,the governor is mechanical,it opens the throttle blades and dumps fuel into the engine,the fuel goes thru the motor and blows up in the muffler which superheats after shutdown.I feel the problem with Bassman's is the carb leaking down,either from a high float level,leaky needle/seat or loose bolts,gaskets.The motor is running rich when its blowing black smole-this is no good for it at all,and washes the cyl down,and dilutes the oil with fuel.The easiest thing to do it buy a new carb and bolt it on.

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