kohler engine loss of power at high idle

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  #1  
Old 09-14-13, 08:55 AM
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kohler engine loss of power at high idle

I have a toro z master zero turn riding mower. It has a kohler engine model Ch25 S. Two weeks ago I had gas coming out of the breather hose, oil from the muffler and gas in the crankcase. I read a older post that explained the problem could be caused by a defective needle valve. When I took the carb apart, I discovered that this was the problem. I replaced the needle valve, changed the oil and filter. I used it two times afterwards, putting about 8 run hours on it. Everything was good. Then quite suddenly I experienced a new set of problems. Loss of power at high idle, a milky white substance that comes out like a fine mist from the breather hose, gas leaking out of one of the cylinder heads where the exhaust connects, and white smoke from the muffler. Any advice on what the problem might be and how to correct it would be much appreciated. Thanks
 
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Old 09-14-13, 09:47 AM
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It's really back to the same thing you started with. You'll have to get the fuel leak stopped, change the oil and you should be fine. It's tough to say why the problem resurfaced.

Sometimes if you have a fuel pump that's pulse driven and the pump diaphragm gets a hole in it, the fuel can enter the crankcase through the pulse port. You see that occasionally in snowmobiles.
 
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Old 09-16-13, 06:29 AM
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Thanks for the advice. I reread my original post. I did not include that I had put on a new fuel pump. I will change the oil as you suggested. Any thoughts about what may cause the fuel leak I mentioned?
 
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Old 09-16-13, 06:48 AM
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On the older style of carburetors it's usually the float/float needle/needle seat - one of those just isn't shutting off the flow of fuel into the bowl. It overfills and floods the engine/crankcase.

A possibility is trash or sediment coming down the fuel line and presenting a reoccurring problem. You might check your filter and the condition of the line to make sure it's not flaking off inside.

Did you put a complete kit in the carb when you worked on it? Cheese zeros in on some maverick "O" ring that seems to be an on going culprit in some types of carburetors.
 
  #5  
Old 09-16-13, 10:22 AM
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Might want to check the compression on both cylinders. If one is drastically lower than the other, you may have a failed piston/ring or even a cracked block. Simple check, gage costs under $25, and it could rule out a major issue.

Same thing happened to the horizontal shaft Briggs engine on my Grasshopper. It would start and idle just fine, then when you put a load on it or tried to hop-up the RPM, it would sputter and spew. Broke a rod and it cracked the block. That cylinder showed 0psi compression. Engine scrapped and mower carcass sold.
 
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Old 09-19-13, 06:35 PM
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I had the chance to check on some of the suggestions I received. Had a friend with a compression gauge. Checked both cylinders. The compression was good on both and no difference in the reading. In regards to the carb. I did not get a kit. However I did discover that a small o-ring was bad on a piece identified as a slow jet. I replaced it and also put on a new carb. body gasket. I did have fuel which entered the crankcase. I changed the oil and put on a new filter. The problem still remains (lack of power at high idle). The carburetor has a part on it, a accelerator pump. I'm not familiar with this. Is it possible that this may be the source of my problem?
 
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Old 09-20-13, 03:38 AM
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An accelerator pump is more of a transition pump that would help idle to mid range rpms steps. You see them on engines that may have a little vacuum lag when the throttle opens up.

Carburetor type automotive applications have them as a norm in one shape or another. In a car engine, when the throttle plates snap open there is a sudden loss of vacuum until the engine picks up revs. The loss of vacuum means a loss of air flow through the venturi and at that point creates a fuel mixture leaning without the accel pump. The pump throws fuel into the air stream to compensate.

If you've having a big lag as the engine steps from high idle to midrange, that pump may be to blame. AS far as the original problem, I don't know if that would be a path for major leakage into the crankcase.
 
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Old 09-24-13, 06:37 AM
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thanks for the explanation on the acc. pump. After reading I agree that does not sound like the cause of the problem. I'm stumped at this point. I've given some thought to a new carb. In any case thanks for the input.
 
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