puttputt Posted April 9, 2019 Posted April 9, 2019 Good day everyone. It will soon be cabin time again here and I have a question about one of my garden tractors I have out there. It's the Sun Star with the 20 horse magnum. Just before I put it away last fall, it developed an issue. The tractor runs fine but if it idles for a couple of minutes, the idle will drop down real low, almost to the point of stalling. But instead of stalling, it will backfire and then idle fine again. If you increase the throttle it runs fine. I didn't have a chance to dig into it last fall so I don't know if could be something as simple as a fine carb adjustment or? I thought before I start looking at it that maybe there might be some suggestions of what it could be. I can't say I noticed any black smoke out the exhaust when it acts up.. It is a new carb on it.
BigNickNY Posted April 9, 2019 Posted April 9, 2019 I would definitely check to make sure there is no water in the fuel (if it wasn't drained before storage) as it could be sucking in water and backfiring while getting more good fuel into its system. Running it at a higher RPM might be clearing it out or sucking more fuel than water. I would check to see if the jets have any sort of debris or rust coating them or if theres anything inside the carb bowl. Hope this helps! Nick 1
puttputt Posted April 9, 2019 Author Posted April 9, 2019 I haven't run it yet this year as I'm not out at the cabin yet. It started doing this last fall before I put it away so I don't think it's a water in the fuel problem. The tractor is also always inside when not in use. But yes, it could be a jet issue so I will pull them when I get out there. But I will also drain the fuel to make sure there is no water.
MikeES Posted April 9, 2019 Posted April 9, 2019 The M20, probably has the fixed jet Walbro carburetor. They can be a bugger when the carb is clean, and a real problem with an older gunked up carb. Because of not having a high speed (main) adjustable jet, it is a fine line to get the low speed adjusted so the tractor idles and yet doesn't bog down or surges at full throttle. Yours sounds like maybe the engine runs fine a faster engine speeds but loads up on long idle. At some point the loading is lowering the engine rpms, until the governor kicks in to speed up, opens the throttle, cleans it's throat, and is good until it starts loading up again. I have a M20 that I could not get to run clean through the full rpm range. My solution was to install a Kohler adjustable jet carb from a KT17. It now has great full rpm power, and you can let it idle for 5+ without killing or loading up. (Note: I have never had any reason to let a tractor idle for much more 5 mins) 1
phillobbezoo Posted April 10, 2019 Posted April 10, 2019 3 hours ago, MikeES said: The M20, probably has the fixed jet Walbro carburetor. They can be a bugger when the carb is clean, and a real problem with an older gunked up carb. Because of not having a high speed (main) adjustable jet, it is a fine line to get the low speed adjusted so the tractor idles and yet doesn't bog down or surges at full throttle. Yours sounds like maybe the engine runs fine a faster engine speeds but loads up on long idle. At some point the loading is lowering the engine rpms, until the governor kicks in to speed up, opens the throttle, cleans it's throat, and is good until it starts loading up again. I have a M20 that I could not get to run clean through the full rpm range. My solution was to install a Kohler adjustable jet carb from a KT17. It now has great full rpm power, and you can let it idle for 5+ without killing or loading up. (Note: I have never had any reason to let a tractor idle for much more 5 mins) I had the same issuies with my m20, couldn’t get it to stop surging at high rpm, and have it idle like it should. I got sick of messing with it and bought a new carb, it’s one of those cheap aftermarket carbs but I’ve had great luck with it so far.
puttputt Posted April 10, 2019 Author Posted April 10, 2019 Mine has a new carb on it, one of those Chinese carbs with adjustable jets. So it could be that I didn't get it set just right. It runs fine otherwise and idles fine until it gets to the point where it starts to drop in idle rpm and backfires. If I get to it quick enough, before it decides to backfire, there is no problem throttling up. So it could very well be that my low speed setting is off or dirt got on the jet/ idle circuit.
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