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midnightpumpkin

Carb Adjustment

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midnightpumpkin
New to me 7013 Shuttle with what appears to be the orginal 13HP engine. The carb had water in it when I got it. Rebuilt the carb. It runs strong and idles down well. The only issue is it wants to stall out if the throttle is moved off idle too quickly. Any ideas? Thanks, John U

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ssmewing
In my experience with other carbs... you are still restricted, somewhere. There is a passage that feeds fuel when you give it more throttle. It may take mechanical poking to get it clear. Or a stronger carb cleaner. Actually when you give it throttle you create a little negative pressure in the carb and it needs to suck gas in to increase fuel flow. Since the fuel is under very little pressure it does not take much to slow it down. You could just use some SEA FOAM in the gas. I have used this stuff and had great results with it. It does a great job cleaning out a running engine.

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dhardin
Your tip off here is water left in carb bowl. ssmewing is right on, its my experience the venture holes in the main jet has 2 or more small holes in the bottom of the tube. These small hole are your ideal gas feed. These small hole could be blocked ever so slightly in one or more has a restriction within then.




This is not a real good example but it dose show what looks to be a operational venture is quite restricted. Most likely not enough to cause a problem as you have. The inside of the tube can be as corroded and restrict the ideal gas flow. So when you accelerate you dump the cylinder with gas then causing what I call a hesitation or stumble.

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midnightpumpkin
I will be heading out to my shop tomorrow to see what I can do with this carburetor. First thing I intend to do is remove the main and Idle adjusters and run carb cleaner through the jets. If that doesn't help, I will remove the emulsion tube and replace it with a brand new one. I did "rod" out the small holes in the emulsion tube with a torch tip cleaner, but I may have missed something. If all that fails, I will take the carb apart and try adjusting the float as Dave suggested. I do have a good carb I can put on, but I would really like to get this one to run right so that I have a spare carb on hand. Thanks to all who responded. John U

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HubbardRA
There is one part of carb adjustment that most people overlook. After doing the left till rough then right till rough, then center (most people stop here). There is one more step. You need to open the throttle quickly and look for hesitation (as you obviously have). When there is hesitation you should open the jet slightly more and try the throttle. Keep opening the jet till the hesitation is gone. Then go back and adjust the idle jet again. I always do mine this way. Since these tractors do not have an accelerator pump, the only way to compensate for the lean condition when the throttle is suddenly opened is by running the main jet a little richer. I have the same tractor, an AC 713S, which has a 13 Hp B/S, not a Kohler.

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ssmewing
I did read an article lately that said a common carb problen in the throttle plate shaft bushings get worn and introduce to much air and in the wrong place giving a lean condition. This was from a carb specialist and in essence he required ever carb rebuild have the bushings either changed or verified to be tight. Without the negative pressure in the right spot you do not draw fuel in. He went on to say that it is the most common reason a fresh rebuild fails. In the case of full throttle operation you run lean which means you run hot. This carb guy builds for Lawn tractor racers. As a side note, sorry Simplicity fans but there is a direct drive CubCadet system that rules by easy margin for race set-up. It is durable and the most effiecient. Through these people there are all kinds of hopup options though.

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midnightpumpkin
I believe I got the problem resolved. I replaced the throttle body with one that had tighter bushing, put in a new emulsion tube with 2 tiny holes at the jet end (the original only had one tiny hole). Once I got it started, I followed Rod's advise. It now takes gas without stumbling. Thanks for all the tips and ideas. John U

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