Trouble With Exmark Kohler CH740 Engine

IndianaJimMay 15, 2013

The engine runs fine all the way up to about half throttle, after that it starts missing out/bogging down, just no power. I've replaced the coils, the spark plugs, the entire carb, the fuel filter, a valve that didn't seem to be seating properly (most likely was fine) I've pulled the flywheel to make sure the keyway wasn't sheared.

It is getting plenty of fuel, seems to be a timing issue almost, at a total loss!!! Any Suggestions???
Thanks
Jim

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mownie(7)

Are you using a Kohler brand fuel filter?
Kohler engines are well known for being extremely picky about their fuel filters.
Some "aftermarket" fuel filters are only made to "look like" the filter they are substituting for, and don't have the specified flow rate.
Personally, I buy a larger inline fuel filter at an auto parts house and I know I am getting sufficient flow rate.
You only need to know the hose diameter (usually 1/4") and choose a filter that IS NOT for a fuel injection system.
The reason fuel injection rated filters for cars should not be used is because you will pay 2X or 3X the price because of their heavier construction.
If you can put up a photo of your spark plugs so we can see the color (which is a reflection of combustion chamber activity) we may be able to see if this is caused by insufficient fuel (or not).

    Bookmark   May 15, 2013 at 11:29AM
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IndianaJim

Yes I'm using an Exmark fuel filter. The fuel is not the problem, getting plenty fuel. Plugs look good.

    Bookmark   May 15, 2013 at 12:00PM
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mownie(7)

I don't think you understand the full implication of my premise on using a genuine Kohler brand filter or the idea that insufficient fuel "at high demand points" may not be indicated when checking at other times.
My point on Kohler brand is that unless the filter comes as a Kohler packaged item, it may not have been sourced from Kohler at all.
Exmark, like lots of other OEMs may offer (as their first choice) a replacement filter bearing the Exmark logo. If that is the case you can bet it was sourced from an aftermarket supplier and not Kohler.
On the other point about insufficient fuel, I mean "how do you know the fuel VOLUME is sufficient at times when demand for fuel is at its peak (under a load at high RPM).
Just because the fuel pump seems to be filling the bowl at cranking or idle RPM, or that the fuel bowl is full when you remove it does not prove that the same things are constant under conditions of high fuel demand.
But on the other hand, I did not see where you have changed the SAM (Spark Advance Module) on this engine.
You might want to take the SAM to a Kohler dealer and see if they have the proprietary Kohler tester to see if it is working right.
That is about the only thing you haven't replaced so far.

    Bookmark   May 15, 2013 at 12:33PM
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IndianaJim

Where is the SAM located, might be on to something. because it seems to me like a timing issue

    Bookmark   May 15, 2013 at 12:49PM
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mownie(7)

Jim, check your e-mail. I sent you a service manual.

    Bookmark   May 15, 2013 at 1:00PM
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IndianaJim

How much does a SAM cost roughly

    Bookmark   May 15, 2013 at 1:19PM
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bill_kapaun

How "fresh" is the fuel?
IF you have water/crud in the gas, it may be sitting on the bottom of the carb bowl until you speed up/load the engine. Then, the increased fuel flow may be enough to "stir up" the crud and allow it THROUGH the carb.

    Bookmark   May 15, 2013 at 2:46PM
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IndianaJim

Fresh fuel, dumped and cleaned the tank before installing new carb

    Bookmark   May 15, 2013 at 3:07PM
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rcbe(6)

didja dbke-chk for the correct type of plugs? a "wrong" type could be breaking down under increased heat/load.... or try spraying some rattlecan carb cleaner around the the intakes and carb connections with engine running at "missing rpm" to spot an air leak....

    Bookmark   May 15, 2013 at 7:49PM
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tomplum

Some of the DSAMs have been replaced with DSAI components. Without the spec, and a better description- there isn't a lot to go on. Could be the root of all evil.It seems to me the Exmark was the subject of current surges when the PTO engages - thus damaging the ignition components. This years and or last years service school notes.
Personally I think there also has been too much read into fuel filters and Kohler engines. I have never seen a model with a pump have issues. Pump filters can be the large canister 13 mic to 51 teardrops. Gravity feed systems can use the teardrop np if there is enough head, but need the small bodied ones (ideally a Kohler part) if not or if problems occur. Like was indicated above- equipment manufacturers don't always put the right stuff in the box! Though a twin has a pump...

    Bookmark   May 15, 2013 at 11:36PM
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mla2ofus

No mention of changing the air filter, which this symptom sounds a lot like.
Mike

    Bookmark   May 16, 2013 at 10:45AM
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mownie(7)

Typically, when a clogged air filter is the culprit, the chief complaints will be:
Heavy exhaust fumes smell and/or BLACK smoke out the muffler.
Spark plugs will be very black, sooty in appearance and may even appear wet or gummy, but the deep black color is the key.
Clogged air filters in themselves do not result in immediate symptoms involving "misfire" or "skipping a beat". But prolonged use of an engine with a clogged air filter can eventually cause misfire or even a dead cylinder due to the carbon (soot) deposits collecting on the spark plug. Eventually that carbon will develop into a conductor path that is easier to follow than jumping the open gap between the 2 electrodes. When that happens.........you don't got no more spark.

    Bookmark   May 16, 2013 at 11:05AM
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