Autochoke link and bi-metalic thermostat

Johns_Pop

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Ok, y'all don't laugh at me when you see the picture of the choke link. I was in the field with no internet access and I figured out what the problem was, but I was not aware that the "spring" the choke link was attached to was actually a thermostat. After taking the cover off a million times I finally realized the arm was in different positions and after screwing with it for a while (and probably buggering it up in the process), I thought, "Hunh..... that thing looks like it's auto-adjusting itself." Can't get nothin by me! :biggrin: I had never seen one of those. ANYWAY..... My autochoke is not working and by the time I tried to adjust that rod a million times, it's been bent into a terrible shape. I might need a new one, but looks like the thermostat is built right into the muffler. My parts manual shows the muffler assembly but doesn't show a separate part number for the thermostat. My muffler appears to be a 300G.

My mower was running raggedy with no power and kept cutting out and at some point I realized it was simply getting way too much fuel and running too rich. Ever since I bought the mower used it's been pouring fuel out of the carb and I thought I had the problem fixed. Once I realized it was running so rich and I started adjusting that arm, the fuel leakage stopped. That choke valve just doesn't seem to want to get in the right position. When I get the mower cranked and it's trying to cut out, I can hold that closed with a screwdriver and the mower will run like a scalded dog. But I know that's too lean. Ever which way I adjusted that linkage, it just seemed to allow the choke to flop and bring me back to the "too rich no power" mode. You think that thermostat is bad? Would that cause this problem?

Pics are of bent up rod, open choke and pics ID'ing my mower and engine. When I started, that rod looked factory new, so yeah. :ashamed:

20170914_153115.jpg20170914_153127.jpg20170915_174725.jpg20170915_174809.jpg20170915_174821.jpg
 

dfbroxy

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Thanks for the post and the info. I have this same mower and had carb problems. Took it on and off cleaning it 4 times before it ran right. With this new info I think the choke linkage must have gotten bent a little and in the process of removeing it 4 times
got fixed. Sometimes its the obvious that trips us up.
 

Johns_Pop

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From what I've been reading the thermostat (that black part on the top of the muffler that linkage connects to) often fails and doesn't operate the choke right. I thought you had to replace the whole muffler, but I think I'm closing in on the right replacement part. :)

Edit: Gah.... I was looking at the wrong part. :( Looks like that's an assembly, the thermostat comes on the muffler, not as a separate part. I need part 592362 to the tune of 28 bucks plus shipping, unless I buy a used one off eBay which I won't know if the thermostat works or not. That's a long way towards a whole new Predator replacement engine at Harbor Freight. Now if one of you gurus can tell me how to rig this thing into a manual choke so I can get it to run reliably, that'd be the trick. ;)
 
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zman111666

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Actually, if I remember right, the biggest mistake with that setup is it's easy to have the linkage laying the wrong way during reassembly, causing the choke to stay closed. I'll have to look to see if I have one in the yard. I wouldn't worry much about that choke thermostat rod, it bends easy enough by hand, so as long as you didn't damage the bimetallic spring in the little round part on the muffler, you'll be alright.
 

zman111666

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Ok, i just checked, and you have the linkage right, you just got to re-bend the rod so it looks more like the one in the picture. The way you got it, it is too straight, and pushing too hard on the choke. Got to bend it to shorten it up.

carbLink1.jpgCarbLink2.jpg
 

Johns_Pop

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I've bent that thing a hundred different ways. :) I really think that thermostat in there is no good.
 

EngineMan

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I've bent that thing a hundred different ways. :) I really think that thermostat in there is no good.

Then put some heat on it and see if it moves, and if it doesn't, replace it...!
 

Johns_Pop

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It moves. I don't think it's moving reliably though because no matter how I adjust the linkage, it's not operating the choke reliably. Sometimes it opens all the way and the mower runs too rich and it floods the carburetor, eventually dying. If I take all the slack off the linkage the choke just flops back and forth and the mower sputters and coughs the whole time and it eventually dies. I can't get it to close the choke far enough to lean out like it should and stay there. I thought about just plugging the choke shut, but then it runs way too fast and I'm pretty sure it'll destroy the engine pretty quick running that fast. Maybe I have a spring issue or a governor issue, but I was so focused on this autochoke linkage that I'm missing it. The thermostat is moving the linkage back and forth as it heats and cools, but I can't get this thing to run worth a darn. I've cleaned the carburetor and everything looks good in there and as I've said, if I hold that choke closed or in the proper position the mower will run flawlessly, so I don't think it's carb related at least internally. Hopefully I'll get a chance to work on it this weekend and I'll post a couple short videos on youtube and link them here. I appreciate the help.
 

EngineMan

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It moves. I don't think it's moving reliably though because no matter how I adjust the linkage, it's not operating the choke reliably. Sometimes it opens all the way and the mower runs too rich and it floods the carburetor, eventually dying. If I take all the slack off the linkage the choke just flops back and forth and the mower sputters and coughs the whole time and it eventually dies. I can't get it to close the choke far enough to lean out like it should and stay there. I thought about just plugging the choke shut, but then it runs way too fast and I'm pretty sure it'll destroy the engine pretty quick running that fast. Maybe I have a spring issue or a governor issue, but I was so focused on this autochoke linkage that I'm missing it. The thermostat is moving the linkage back and forth as it heats and cools, but I can't get this thing to run worth a darn. I've cleaned the carburetor and everything looks good in there and as I've said, if I hold that choke closed or in the proper position the mower will run flawlessly, so I don't think it's carb related at least internally. Hopefully I'll get a chance to work on it this weekend and I'll post a couple short videos on youtube and link them here. I appreciate the help.

When the engine is at running temperature, the choke should be fully open and not like you say fully "closed", are you confusing yourself with the throttle shutter..?

when the engine is cold the choke shutter should be closed, and then open up when the engine get's warm. it should not run rich or should flood the carburetor when the choke is open, if the carburetor if flooding then you need to check it out again, (inlet needle valve or float)

"the Bi-metal spring aids the choke in staying closed to augment cold starts and
assists the choke in opening when the engine is warm."
 

Johns_Pop

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When the engine is at running temperature, the choke should be fully open and not like you say fully "closed", are you confusing yourself with the throttle shutter..?

Maybe, I don't know to be honest. There's a shutter inside the carb that I can't see when the carb is installed on the mower. Then there's a shutter right there on the outside of the carb, which I posted a picture of, that you can see when you take the air filter off. When that is open, the mower runs ragged and gets way too much fuel. When it is approaching closed, the mower runs better, but the spring/arm is allowing it to flop back and forth and it is still too rich and sputtering eventually losing power to where the engine dies. If I take a screwdriver and hold that shutter closed, the mower runs at top speed with no sputtering at all, but it's running to fast for me to just manually close that up. I can pretty much get the mower started whether it's cold or warm, but it just won't run worth a squat. Again, I'll post a video soon that shows what it's doing as I'm sure that'll show much more accurately the symptoms versus my ignorant ramblings. :smile: I understand the basics of how engines operate, but I'm still learning the nuances of all the various systems on all these various mowers. I wish they'd all come up with something that works and leave well enough alone. I've got 5 push mowers, 4 of them the same brand, and every single one of them handle the choke and throttle differently. (sigh) I don't mind learning, I just have a hard time keeping up with all the changes the older I get. :confused2:
 
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