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heron

Sunstar/ Kohler CH20S stalling out?

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heron
Ran my somewhat newly acquired 97 Sunstar today for the first real hard cut day. Tractor has 590 hours, seemed to run great today for the first hour of pretty hard(thick) cutting. Let it idle down just a bit before shutting it off to walk an area before I cut it and heard a sharp backfire. Started up fine and ran the same so at that point I took it over and gassed it up with 93 Non-Ethanol gas. Returned to the same area to finish cutting and the mower began to lose rpm and then gain it again and so on. Decided to quit for the evening and clean it up. Any ideas what it could be with this Kohler? 1. Got the new gas from a station up the road...maybe water? 2. I did put a new filter and synthetic oil in but used a Wix oil filter. The reason I say this is because it seemed difficult trying to get the level right and I though maybe since the Wix had the spring it was not letting oil in to the filter right away when I first added the oil hence I ran it a little low and the oil Sentry was cutting on and off...? I know it takes 2.1 quarts but I was pouring out of a 5 qt container. 3. Could it be vapor locking..it was hot today...85 and I did add the gas when it was hot..is this something common with this engine? 4. Backfiring screwed something up in the carb? 5. Maybe when I added about 3 gallons of the gas it stirred something up and plugged the gas filter..? Plugs, air filter etc...all new. It ran strong for a good bit..hopefully it's something simple. I did put a "Kohler" oil filter back on it and put some gas treatment in tonight. I did have to clean out the pre-filter..it was pretty dirty after cutting up all the leaves..dust,dust, dust today. What do you fellas think?

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Tarheel
Back when those units were new, (with Magnum engines) I ran into a number of them acting that way. On these, you could partly choke them and they would clear up for a minute but then got worse than ever. They were starving for fuel. Ended up replacing the fuel pumps on them.

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RayS
Don`t know if this is the problem. If it has a fuel shut off solenoid you will want to shut it down according to the service repair manual. At full to half throttle. It will backfire otherwise at times and can blow a head gasket. Been there and it is not cheap.


From the CH18 - CH26 horizontal shaft Command owners manual.

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heron
Yes, did shut if off and have since my short ownership of it at half or better throttle...still backfired. I'm changing gas filter tonight and I'll see how it goes. Problem is that if I had not had the backfire I would be sure it was the new gas but since it backfired..then I gassed it up I'm not sure what the culprit is. Does the backfire always do in the head gasket? What are signs of a bad gasket on this motor? I did notice when driving it back to gas can it sputtered a bit so maybe it was just real low on gas and sucked some air right before I filled it up....?

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RayS
I would say no. Mine backfired off and on for 2 years before it blew the gasket. Only reason I mentioned it is that you stated that you "Let it idle down just a bit before shutting it off".

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heron
Thanks Ray...I was sweating at the thought of having to do a gasket on this motor. It seemed to run fine after awhile but I was done cutting and loading the motor. Do you know if there is some type of screen at the bottom of the fuel tank on the sunstar? I don't see one on the breakdown. I may hit the carb with some carb cleaner to see if I can free any junk up also.

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heron
Can someone help me out on this carburetor. Not sure how it's supposed to work but there is a jet under the choke flap and when I'm at mid throttle the gas kind of sprays out UN-uniformly and as it pulses the motor revs up and down somewhat erratically which is something I asked about when I first acquired this tractor. Not sure how these V-twins work or are expected to work but I always looked for even sprays when I worked on Holley's or Quadrajets. This spray is sporatic at best but when I throttle it all the way up I can just see dripping down to the lower flap...? I've used seafoam and gumout treatment in the gas...wondering if there is a easy way to pull these carbs apart and clean them without opening up a can of worms. Also, could this be a weak fuel pump causing the eratic behavior and maybe even the original issue..maybe once the motor heats up to a certain level the pump fades...?

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comet66
I've never had a carb problem with my Kohlers so I can't answer that question. I have had similar symptoms though. Loss of power, surging, give it a little choke and it seems to get a bit better. You might try pulling the plug wires one at a time and see if it makes any difference in the way it runs. If one consistently makes no difference, and the other stalls the engine, you could have an ignition module failing. I've replaced three over the years. Kind of a pain, but not difficult, and a good chance to get under the covers and clean things up. Keep us posted on what you find.

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heron
Acfarmer: I've never heard that on the Super Unleaded gas..I would think better combustion would create less carbon. Better explosion=more heat, less build up. Can you explain further? Also, yes, I use seafoam quite a bit and have in this machine. Do these Kohlers just run not so smooth until you idle them up? I thought I remember my dads 71 T-16 Homelite with the single cylinder Briggs running smoother than this Kohler.

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