# Made a carb adjmt



## Mickey (Aug 14, 2010)

Posted about a problem I had a few days back about my Cub. When I pulled the carb I didn't notice any external adjmt screws for low speed fuel mixture. Since early days of owning this Cub I've not been happy with the way the engine shuts down after some hard work. It backfires and I believe runs backwards. Anyway I've been concerned over the possibility of throwing a rod or something similar. I've tried to min this by shortly after turning off the key to throw the throttle wide open. Seems to help unless I'm a little slow on opening the throttle.

Well, anyway I get looking through my service manual for this Kohler and noticed a callout in the carb section for a low speed adjmt. Pulled the carb off again this morning and no adjmt screw seen but I did find a plug where I thought the adjmt screw should have been located. Pulled the plug off the carb and low and behold there is a screw behind the plug. Manual said starting point for adjmt was 1.5 turn open. When I went to check I found the screw fully seated. No wonder engine running so lean it would cause the backfiring. Next set the screw 1.5 turns open and put the carb back together. Engine seems to start better and after putting the tractor to work, I then shut the engine down. *SO* much better. Will have to use the tractor some more to be sure but by fact I left the plug off the carb, if it needs further adjmt, it will be a lot easier than before.

So, if you have a Kohler V-twin and you're not happy with the way it shuts off, there is hope. Pop the plug and get access to the adj screw.

Manual says start with screw open 1.5 turns. With engine warn, turn the screw in until engine noticebly slows down then open the screw 3/4 turn.

I remember back in the day, low speed mixture screw always started with screw open 1.5 - 2 turns then use vac gauge to adj for max speed. This applied to small engines with real carbs, not those mickey-mouse B&S ones, and even cars.


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## Country Boy (Mar 18, 2010)

Are you sure that's an adjustment needle and not a jet? I know Tecumseh put a cap on when they went from an adjustable needle to a fixed jet so no one would move it. If there is a spring on the screw, then its probably a needle. If not, its probably a jet and should be seated all the way in. You can take it out and see if its a tapered needle or a plug with a hole in it. Most of the newer carbs built in the last 10-15 years don't have any adjustments for the mixture. Some of the older Command series Kohler engines did, but I haven't seen one on a new Kohler (or other brands) in years. Kohler says in their instruction manual to let the engine idle for a few minutes after working it, then run it up to about 2/3-3/4 throttle before shutting it down. What happens is that the engine gets so hot that the fuel ignites on its own in the cylinders and muffler. Letting it idle will cool the engine and prevent the dieseling you are hearing. My gas farm tractors do the same thing when you get them good and hot in the fields. The only solution is to let them idle a bit before shutting them down. We have a septic tank pumping company in the area that was complaining about their 30hp Kohler doing the same thing as your tractor. He would work it hard in an enclosed space (engine is mounted in a box under the tanker), then let it idle about 20 seconds and shut it off. It would backfire and diesel like crazy. I kept telling him he has to let it idle for several minutes to cool it down, but he didn't seem to listen. He was going to re-do the guard around the belt pulley to allow more air flow around the engine which should help a lot.


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## farmertim (Dec 1, 2010)

Aah bring back the old decompressor lever.


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## Mickey (Aug 14, 2010)

Country Boy said:


> *Are you sure that's an adjustment needle and not a jet?* I know Tecumseh put a cap on when they went from an adjustable needle to a fixed jet so no one would move it. If there is a spring on the screw, then its probably a needle. If not, its probably a jet and should be seated all the way in. You can take it out and see if its a tapered needle or a plug with a hole in it. ..........


Sorry my composition was so poor I wasn't clear enough for you. Maybe this will help. Straight from the manual.


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## Country Boy (Mar 18, 2010)

Just checking. I had several people "adjust" their Tecumseh fixed jet carbs by loosening the idle jet. They brought them in to me because the adjustment didn't work and I had to explain that the carbs are fixed jet and not adjustable. Not too many carbs let you adjust the mixture anymore. Lawnboy used to hide the idle jet behind a sticker on their later two-cycle engine carbs. Once I discovered that, I was able to save several carbs that would otherwise have been replaced due to poor running. Even your engine had the adjustment hidden behind a plug. Its only going to get worse when the new emission standards come due in January of 2014.


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