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Kohler 20hp Magnum - Engine Surge

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I recently started my tractor (Yardman 20hp/50"deck) for the spring season, and after approx. 90 minutes of running, the engine rpm's started to surge up and down. With obvious loss of power, I found that by pulling the choke out (sometimes fully) I could get the engine rpm's to stabilize, but only for a short time. Even now, with the pto disengaged, the rpm's surge at idle. Without the power needed, I can't use the tractor until I isolate this problem. Any suggestions as to what to look for?

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HubbardRA
It sounds like you left the carb full of gas during the winter and ended up with a varnish build-up in the main jet. This makes the hole in the jet smaller, and thus makes the engine run "lean". If the jet is adjustable on this engine, then adjust it richer. If there is no main jet adjustment, then you must remove the main jet and clean it a small drill bit or pice of hard wire. Do not use the fluted end of the drill bit, use the smooth end. You want to remove the varnish, but don't want to alter the hole in the jet. Rod H.

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MPH
Besides the good advice of checking the carb and adjustment, I would also possibly check the following: 1¤Check the fuel filter if there is one ¥may need to be replaced¤© 2¤Check the gas tank cap to make sure that the vents are clear ¥if it is a vented cap¤© If the vents are not clear the engine could be trying to suck gas against a created vacuum or in the other case the gas vapors could be pushing to much gas into the carb system© This was my assumption when, like you, my engine started running rough after about an hour on a warm day© Shut down the tractor and carefully opened the gas cap and saw beaucoup gas vapors escaping© Cleared the gas cap vents - problem went away© 3¤I add some gas treatment ¥non-alcohol¤ to my fuel can every fillup -- about 3©5oz to 6gal gas can since the 12oz bottle is really for use in a 20gal gas tank© Following the above "adjustments", the engine has never run better©

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    • Dean McFadden

      Dean McFadden

      Good morning peeps! I’m always searching for helpful information with my AC collection. Hope to find out new information and pass on my own experience in restoration. Here are some pics of my babies. I’m still looking for front rims for the 410 so yesterday I put the 310 wheels on took it for a drive. Working pretty good but still needs some carb work. Gotta get the 310 running next. Have a great day!😁
       

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    • thedaddycat

      thedaddycat  »  SmilinSam

      It's in pretty sad shape, but yes I have a yellow plastic cap that I'm fairly certain is what you need. PM me your details and I'll get it out to you.
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