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Hello everyone!

I'm working on a Toro Mower with a Kohler Engine on it for a neighbor. He brought it to me because it wouldn't start. I flushed his water-contaminated gas out and cleaned carb/main jet/emulsion tube. Started right up first pull with some new gas in it... but after a minute it started sputtering and spitting black smoke periodically. I realized that the auto choke was not opening nearly enough and as a result it runs too rich when it warms up. The auto choke is the one like this:

NOT like this:

(For reference)

I had removed the auto choke to get the carburetor off for cleaning but I installed it correctly again (I can tell because as it warms up the arm moves slightly in the right direction but not enough). If I manually release the choke all the way it runs correctly. To test the thermostat or "thermistor" I removed it again and heated it with a lighter. It has full range of motion when heated in this way and doesn't bind up. The linkage that goes to the carburetor is free/not binding and the choke on the carburetor itself moves freely. I added some WD40 to it to see if that would help, but nothing. It's no better. I'm thinking he'll have to buy a new thermostat/autochoke but I wanted to see if anyone has tips/ideas to get them to work again first. I've heard this is a common problem with Kohler push mower engines. It also pops and sputters when you let go of the handle, which I believe is another common issue. I wish Kohler would stick to making toilets. Although their "courage" motors with the oil pan on top are called 0toilet bowl motors by the local shops... so I guess be careful what you wish for. They seem to make decent commercial engines but I hate all of Kohler's residential engines minus maybe the old commands. Anyway, thanks in advance for any advice!

Please give us the model and serial numbers for the mowers. When these units first came out there was a problem with the auto choke not opening properly. If the unit fits into the serial number range I may have a possible solution for you. Also, does the choke fully open when the engine gets to operating temperature?

Model: PH-XT675-2087 Serial: 4427211398 I forced the choke open by taping the linkage that runs across the front to the blower cover so that it could run proper and warm up. It still didn't open fully. After removing the tape 5 minutes later it went right back to running rich.

Put a manual choke cable on it. Problem solved. Stop trying to fix these new super mower sales gimmicks. It will fail again in the future.

slomo

slomo said:

Put a manual choke cable on it. Problem solved. Stop trying to fix these new super mower sales gimmicks. It will fail again in the future.

slomo

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Absolutely something I'd do if it was mine. I even replaced the throttle & choke combination lever with separate throttle and choke controls on my lawn tractor. It's always been stupid to me that they want you to start the engine on full throttle before warming up. Anyway, since it's for my neighbor (and people nowadays struggle to use chokes and primers on equipment that's supposed to have it in the first place) I'll probably replace the mechanism. Maybe it only lasts a few years, but that's about the extent of how long people keep mowers around. Thanks for the advice though!

I had this same issue with Toro belonging to a friend of mine. It appeared the muffler was not getting hot enough to turn the thermistor arm, even with the thermistor being a new one. My last resort was to drill four small holes in the top of the muffler with a 1/8” drill bit. The holes were located where the thermistor sits on the muffler. After re-mounting the thermistor over the holes and tightening the nuts, I started the engine and the thermistor arm began to open the choke as the engine warmed to operating temperature. Within a minute the choke was open fully. Heat conduction did not work, but heating the thermistor with exhaust emissions worked to a tee!

elmrfudd said:

I had this same issue with Toro belonging to a friend of mine. It appeared the muffler was not getting hot enough to turn the thermistor arm, even with the thermistor being a new one. My last resort was to drill four small holes in the top of the muffler with a 1/8” drill bit. The holes were located where the thermistor sits on the muffler. After re-mounting the thermistor over the holes and tightening the nuts, I started the engine and the thermistor arm began to open the choke as the engine warmed to operating temperature. Within a minute the choke was open fully. Heat conduction did not work, but heating the thermistor with exhaust emissions worked to a tee!

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Great job on the fix.

slomo

I absolutely love these auto chokes.
Mean time between failures seems to be about 3 years so the customer actually brings in the mower in place of running it till the oil turns to treacle .
After I have replaced it at least twice, most ask if it can be bypassed

FIXED!!!!!
I was about to throw in the towel with this one, as it seemed like converting to manual choke was a hassle and added expense. My thought was, “How do I make this thermistor get hotter, to the point it will function normally?” I had already tested the thermistor with a small flame, and it functioned as it should. So I was trying to come up with a way to increase the heat to the thermistor. THEN GOD STEPPED IN! He gave me the answer! That’s when I drilled the small holes in the muffler where the thermistor mounts. I could not figure out why the muffler was always hot enough to operate the auto choke before, but not now. Nevertheless, the fix worked like a charm, and my friend was “happy as a lark”!