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25 HP Kohler Command Pops, back fires and misses under a load.

Discussion in 'Mechanic and Repair' started by LawnMower, Sep 12, 2009.

  1. LawnMower

    LawnMower LawnSite Senior Member
    Messages: 653

    25 HP Kohler Command on a Bob Cat, Pops, back fires, and misses under a load. This happens at all engine temps. It almost seems like a bad valve.

    We did a compression check and were getting about 190 pounds on each cylinder.

    The exhaust smells like its running lean. I cant find any screws on the carburetor to adjust the mixture.

    It could be a coil problem, but I'm not sure how to check for that.

    Any advice would be appreciated

  2. ricky86

    ricky86 LawnSite Silver Member
    Messages: 2,123

    I assume it is a CV-25. A twin Command will have about 150 psi when in good shape. I think your gauge is a bit optimistic or there might be a problem with the compression release (will have no effect on running but will be murder on starters) Get a service manual, and follow the instruction for checking the timing. There is a possibility that the spark advance system is a fault. Could be as simple as a loose connection. FOLLOW THE DIRECTIONS.
    One word of caution, it is a C/D system and it will knock you on you butt if you get zapped. Extremely high voltage.
  3. LawnMower

    LawnMower LawnSite Senior Member
    Messages: 653

    Where can I get a manual? Isn't that some only the dealer can get?

    Thanks for the response.
  4. LawnMower

    LawnMower LawnSite Senior Member
    Messages: 653

    I just checked and the Kohler web site has on line manuals that you can read right on the computer. Nice.
  5. East Coast Lawn Choppers

    East Coast Lawn Choppers LawnSite Member
    Messages: 134

    You didn't say if it was a CV25 or CH25, but I have never seen one with a ACR (auto comp release) as far as the popping and hissing it can be a lot of things...
    We just tore apart one that was using oil slightly and the #1 plug had become so oil caked that is was not firing good (but was firing) and it popped and carried on.
    We have had some with burn't intake valves.
    We had a few that had a worn lifter and lobe on the exhaust which forced the burn't gases to try to escape out of the intake on it's stroke.
    We had one so far that the timing advance didn't work.
    Carburation can also be a problem, pull off the carb and clean it, but I'd check a few other things first.
    Do you have access to a leak down checker. If you fill the cylinder on compression stroke (or with the rockers off) you can see if it has a bad valve or bad rings.
    It could be a lot of things.
    The full maual, owner, parts and sevice are all online.
    Let us know your results
  6. PennaLawn

    PennaLawn LawnSite Member
    Messages: 6

    Just one thought fellows, I have had both engines, the one thing that I have found is the way Kohler runs there plug wires around the shielding on the engine has cost me 750.00$ IN A SHORT BLOCK! there are some really dumb rub spots that can cause a momentary short if the engine is under load. Check the entire lenth of both plug wires back to the coils and see if you don't have a bad rub? Just a thought.
  7. VegetiveSteam

    VegetiveSteam LawnSite Senior Member
    Messages: 296

    What is the model number of your engine? The service manual is available at Kohlerplus.com. Click on enter as a guest and go to service literature. 190 lbs of compression is a little high but definitely not impossible. The Command twin doesn't have a compression release (except in special applications) so your minimum compression should be around 150. Typically they run 170 to 180. If I couldn't find anything like a bad plug or something simple like that I'd probably check the flywheel key. Not an extremely common issue but it does happen.
  8. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    The other thing that comes to mind is the rubber pcv line...
    Not sure if that particular model has one, but if it does, inspect for cracks / deterioration.

    If that rubber pcv tube leaks air, the engine will run like crap, the symptoms vary, replace if in doubt.
  9. VegetiveSteam

    VegetiveSteam LawnSite Senior Member
    Messages: 296

    I'm sorry to disagree with you on this but that breather tube, which this engine does have, will have no affect at all on how the engine runs. The only affect it would have is if you run the engine without it or with it cracked it lets the engine suck in unfiltered air and will eventually dirt gut the engine. Other than that the engine should run no different with or without that tube.

    JABBERS LawnSite Senior Member
    from Ohio
    Messages: 459

    I had the same miss on my 26 efi kohlar with 1700 hours. This thing would come and go for 4 years finally i've had it. I replaced 1 coil which helped. My rocker arm came off that was fixed. Still had that same miss now and then so I replaced the lifters, I'll see today if its fixed.

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