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Tuning a Kohler Carbureter
I have a riding mower with a 46' deck powered by a 18.5 hp Kohler Command twin cylinder engine. The carburetor continually needs tuning. I don't know how to tune it properly and just fiddle until it seems right. There are three possible adjustment screws. One is the screw that operates a needle valve that closes / opens as the float in the float bowl moves up and down. I call this the float adjustment. The second is further down the line in the mixing process, I dont really know what it does as I have not been able to completely disassemble the carburetor and just fiddle with it. The third looks like it is the idle adjustment, it changes how soon the cable connected to the throttle comes to rest when the engine idles down. Its essentially adjusting the position a lever rests at (lowest point), I call this the idle screw. The engine continually seems to operate roughly and often backfires, I make some adjustments and all works fine for a while. At the moment the exhaust smells of fuel so I think it is running rich. I bought a book on small engine repair but they dont give any help on how to tune a carburetor. How is it done, where do you start and how should I proceed. I found quite a bit of sediment in the carb float bowl and have replaced the fuel filter and cleaned everything out but I still cant get it back to normal. All suggestions are welcome as is a description of how to tune the sucker.
Thanks in advance, AB
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Tuning a Kohler Carbureter
I had a briggs 8 HP log splitter that was the same way. It never ran great from the day it was brand new 14 years ago, and went in for warranty work 2 times, never to be fixed properly. It would run great for a day or 2 at the most, then require adjusting the mix screw to make it run good again. The float valve never worked and leaked all fuel out when not running. One day it needed leaner, the next richer, and then back. I gave it the best tune up money could buy, a Honda 8HP. I learned my lesson with Hondas a few years ago: always buy them and forget about the junk. Now it always runs great. Besides those drastic measures, I would forget about the idle speed screw unless when it runs, it runs too slow or fast. The float adjustment is a poassible problem but I doubt it. I usually take the carb off, turn the mix screw in all the way counting the turns to all the way in so you know where to set it later. Then take that screw all the way out. On my older Kohlers, that screw is hollow and has holes so I clean them with carb cleaner and a single strand of copper wire to poke out the dirt. I spray carb cleaner through all orifices and remove float valve and clean it and its seat. Then put it back and see how it works, adjusting the mix screw at an idle to get it smooth. Your newer bigger engine is probably different than mine and I don't have the manual for it so I can't tell you the settings for the mix screw.
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Tuning a Kohler Carbureter
I have a couple of 18HP Kohler Commands in my 1862 and 1864 Cadet mowers with 46" decks along with (4) 17 HP Kohlers in older Cadets. All of them seem to run "rich" at an idle. You could have several problems.
If you noticed debris in the carb and changed the fuel filter, some residue is likely in the fuel line between the fuel filter and carb and you may be recontaminating it. Getting junk in the carb affects performance and can keep the needle valve and float mechanism open a tiny portion causing some flooding. I'd suggest cleaning it again and flushing the line between the filter and carb. I would also suggest replacing the needle valve and seat since they are not that expensive. It is a common engine so these parts should be easy to get.
Another component is the air filter, if it is clogged sufficient air can't mix with the fuel.
My dealer told me that the Kohler engine has fixed porting so you can't change the fuel mix at operating speed but can play with the idle adjustment.
If you turn this model off quickly after doing some work without a 1 to 2 minute idle cool down, it generally will backfire and diesel.
If I remember correctly, there is a screw for idle adjustment that controls the idle RPM. There is also a governor adjustment which is a spring attached to a lever. There are several spring attachment points. I wouldn't mess with that unless you think someone has been messing with it earlier. If while idling, the governor is substantially reacting to keep it running, it is out of adjustment.
If you have a carb that has an orifice adjustment, you can turn it in until it begins to run rough, then open it counting the screw rev's until it runs rough again. Then turn it back into the middle position or half the screw rev's.
If it is running too rich, tighten the screw until is runs rough and then back up the screw position 1/4 to 1/2 rev.
Those are the two steps my dad taught me. If that don't work, step three is take it to a good lawnmower shop. There is nothing wrong with the Kohler that can't be easily repaired. My commands have about 500 hours on them and my old 17 HP's have up to 1700 hrs.
P.S. Many engines run differently in winter months running especially "rich". One of my 17 HP's exhibited a carb freeze-up situation until the air intake got a flexible hose attached to it warming it up from a bracket on the exhaust manifold to preheat the intake. You could actually see the frost build-up on the outside of the carb, the float would stick open and just dump gas. It would go through a tank of gas in less than an hour and wash down the cylinder walls and collect in the pan. The pan would fill up until the engine wouldn't run anymore.
Hope this helps!
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Tuning a Kohler Carbureter
Go buy a carb rebuild kit. The rebuild kit will come with diaphragms(2), gasket(2) and needle valve. Install the new needle valve with the float then turn the carb upside down. The float should be parallel the the carb body. Install the new diaphragms and then reinstall the carb. Adjust your air fuel mixture screw all the way in then out 1.5 times to start with. Then turn in or out as needed.
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Tuning a Kohler Carbureter
I can almost guarantee it's a worn throttle shaft. I have had several Kohlers that at around 500-700 hours just don't cooperate. They backfire, sometimes run good sometimes run lousey and are finiky.
I pull my Carbs off and bring them to the mower shop where they replace the throttle shaft and they are good as new.
In general, a carb will rarely need adjustment unless a screw backs out. They need cleaning on occasion. The throttle shaft is the weak link of the kohler.....Jim
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Tuning a Kohler Carbureter
What is a "throttle shaft" ?
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Tuning a Kohler Carbureter
on the kohler where the throttle cable attaches, there is a shaft that goes down into the carb. They wear out and need to be replaced.
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Tuning a Kohler Carbureter
That is news news to me. I probably rebuilt hundreds of carbs and never replaced any thing like that on them.
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Tuning a Kohler Carbureter
The older K series rip through them like crazy. They just get plain eratic and won't run regardless of adjustment. they wear and then I guess it sucks some air or something, Knight's power Equipment turned me on to this a few year back and saved me a lot of grief.
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