1968 Cub 124 - Kohler K301 carburetor issues?

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Jack2468

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I have recently picked up an old Cub 124 garden tractor with the K301 Kohler 12hp engine as a project to fix up, I got it running but it spits and sputters and backfires at times. Also, I think I can see fuel blowing out the carb as well. It seems to run ok once it reaches a certain RPM but any higher or lower than the "sweet spot" and it starts running rough. At lower RPMs, it also someems to run really rich and blow a steady, but light stream of black smoke out the exhaust.

If the throttle lever is all the way down, it stalls, and if you max the throttle out, it just sounds like it's popping off the rev limiter.

The carb looks ok from a visual inspection, it has a new spark plug gapped to spec, fressh gas, fresh oil, and I've inspected all wiring and fuel lines and they look ok.

I haven't tried adjusting the carburetor yet, but would my tractor benefit from just a carb adjustment or will I likely need to rebuild/replace the carb? I'm not super familiar with carburetors, as I've never really needed to mess with one before. All other lawn equipment I have has not needed it.
 
I would simply buy a new carb for $20, that's what I have done for My Wheelhorse with a Kohler M10 and a few other things.
 
Originally Posted By: 123Saab
I would simply buy a new carb for $20, that's what I have done for My Wheelhorse with a Kohler M10 and a few other things.


link?

The carb to my deere 212 wasnt $20 for sure :)(that I could find anyway)
 
I had a Kohler on a CubCadet 108. When it did that stuff it was a burnt exhaust valve. It takes a Stellite valve to hold up to the unleaded gas. Valve was not cheap but after 2 regular valves burnt, never had another issue with the new one.
 
You can try adjusting the carb. The big screw on top is the high speed mixture, turn it in (leaner) to get rid of black smoke, and keep going until it starts to starve, then turn back to a little richer. Do that first.

Then the the screw on the side is the low speed mixture. Hold the throttle plate nearly closed and turn to adjust for best run. If it won't run slow at all, the low speed circuit is probably clogged.

Removing the carb to clean it would be part of any service of a long-unused machine that doesn't run right.
 
I'll give that a shot, thank you. I knew the two screws on the carb adjusted the air/fuel mix but I didn't know which one does what. This was really helpful. I'll try and adjust it and maybe run some fuel cleaner through the tank first, and if it doesn't, then I'll take it apart and try and see what's up with it.
 
Thank you all, I'll try adjusting and using a fuel cleaner first. Then take it apart and clean if that doesn't work. I really hope it isn't a valve issue. It seems to run pretty good once it warms up and you get it to a certain RPM range. It's just when the engine speeds gets above or below that sweet spot, it starts running rough.
 
Originally Posted By: 123Saab
I would simply buy a new carb for $20, that's what I have done for My Wheelhorse with a Kohler M10 and a few other things.

A carb for a 1968 engine is going to be either non existant or very expensive. I doubt 20 dollars. There isn't any demand for anyone to make a carb for something so old.
 
Last edited:
Originally Posted By: Lubener
Originally Posted By: 123Saab
I would simply buy a new carb for $20, that's what I have done for My Wheelhorse with a Kohler M10 and a few other things.

A carb for a 1968 engine is going to be either non existant or very expensive. I doubt 20 dollars. There isn't any demand for anyone to make a carb for something so old.


Originally Posted By: 123Saab
Originally Posted By: Rand
Originally Posted By: 123Saab
I would simply buy a new carb for $20, that's what I have done for My Wheelhorse with a Kohler M10 and a few other things.


link?

The carb to my deere 212 wasnt $20 for sure :)(that I could find anyway)


https://www.amazon.com/Kohler-K241-K301-Cast-Carburetor/dp/B0184E3FT6
 
I'd check the valves as others mentioned, and if that is good I would try cleaning/rebuilding the original carb first. Those cheap ebay carbs work fine but a lot of the time they just don't run quite as smooth as a good working OEM carb.
 
Alright, so I tried adjusting the carb today and it no longer stalls out, also runs very good at low to mid RPMs, but it still pops and bangs and backfires at high RPM. It also seems like it runs very hot, although I do not have an IR thermometer gun to actually measure the temps.
 
That sounds like the carb needs cleaning. It probably has some varnish or ethanol crud causing restrictions.
 
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