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Kohler CV730 looses power uphill under load

Discussion in 'Mechanic and Repair' started by strysnie, Apr 10, 2007.

  1. strysnie

    strysnie LawnSite Member
    Posts: 8

    My first post here, I've read lots of useful info but cannot find anything on the problem I am having.

    Motor is a Kohler CV730, 25hp in a Sears tractor. About 250 hours on it, all maintenance up to date. Recently replaced a head gasket, but the problem I am about to describe was the same before and after I did the head gasket.

    Problem is I loose power/RPMs under load going uphill. Even slight grades are an issue. Steeper grades take me to the point of stalling unless I slow to a crawl. The same grades are not an issue if the deck is disengaged, so without that extra load there is no problem.

    There are no obvious external signs from the motor, no backfiring, no missing, no smoke. It just progressively slows until I remove some load by going really slow or disengaging the deck. The problem clears within a few seconds when I return to level or turn downhill or disengage the deck.

    I dropped the deck, cleaned, and inspected all of the bearings and belts. Everything is fine, no loose bearings, all spin smoothly by hand. I think this rules out excessive load from the deck components.

    Next thought was fuel starvation so I pulled the carb, float level matches spec, and everything is clean. Fuel system is clean all the way from tank to carb and fuel filter is new. I swapped the fuel pump from a working tractor but this made no difference. Air filter is new as well. The choke, throttle, and governor mechanisms appear to be working correctly.

    Plugs look fine, dark grey but no oil or soot, I'm not thinking they are indicating overly lean or rich. Battery is healthy with a full charge.

    I'm going to make a leakdown tester next to see if there is a valve or ring issue, but I really do not expect anything here with only 250 hours on it. When I had the one head off to replace the gasket the cylinder and valves looked pristine.

    Has anyone experienced something like this? Any troubleshooting tips?
  2. ChadsLawn

    ChadsLawn LawnSite Bronze Member
    Posts: 1,110

    Sounds to like maybe your trying to cut tall/thick grass too fast. Is the deck getting clogged when your cutting? That could also be part of the problem.

    Is the govenor(sp) set properlly?

    Thats about all I can think of at the moment. Hope it helps..
  3. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    Put a set of plugs in it. You may have one breaking down under full load. It's harder for a spark to jump a rich environment. If that does'nt do it I have one more thing to try. Sounds like you covered most of the obvious areas.
  4. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    The floor is your's khouse....

    strysnie, Welcome to LawnSite !

    That's some good trouble shooting you performed and a well put together thread.
  5. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    Well, my first thought was that it was starving for fuel. But he said he had checked that. So then I thought that one plug was breaking down under load or one coil or coil wire. So I thought the plugs was the easiest thing to eliminate. Then I was going to move to the coils.
  6. strysnie

    strysnie LawnSite Member
    Posts: 8

    Yeah it does behave similar to when trying to cut too much or too quickly. I should have mentioned that I have this problem even when not cutting grass, like going back up a strip that has just been cut. Deck is clean and everything down there is spinning freely so I do not think that is the problem.

    I do believe the governor is set ok but it is hard to say for sure that it is working correctly as I cannot watch it while the problem occurs. It responds as expected when I play with it sitting still. I've been thinking of rigging something up so I can see what the governor is doing when I have the problem, maybe put some kind of indicator on the throttle linkage that I can watch while driving.

  7. strysnie

    strysnie LawnSite Member
    Posts: 8

    I will give that a try, I do have a new pair of plugs on the shelf.

    I also have another working tractor with a Kohler 22, I will look at the coils on that engine to see if I can swap them to eliminate any coil issues.

  8. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    It does'nt sound like your governor has issues. It's just really tough to diagnose engines with written words. If we only could put our butts in the seat and our hands on the engine! One "old farmer" way to check the coils under load is to connect a timing light up to each coil wire. Then watch the light as you pull that hill. This can tell you if the coil is breaking down under load. Don't forget to check both coils. Don't look directly into the timing light as your head will explode!
  9. strysnie

    strysnie LawnSite Member
    Posts: 8

    Thanks guys for the warm welcome and the ideas - I have a few things to try based on the above.

    I did try the new plugs this evening but they did not make a difference. I'll try to get through the other ideas over the next couple of evenings.
  10. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 921

    You said you used a new fuel filter. Did you use the correct KOHLER filter?
    On another website, there have been a couple cases of Kohlers not even starting when the correct KOHLER filter wasn't used. I don't know why, but it's apparently happened for some reason.

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