Kohler k301 runs rich, quits under load

[ccollins0601]

Hi all,
I got a Cub Cadet 1200 last fall that I've been using for snow plowing & hoping to use for mowing in the spring.

The problem is when under heavy load it tends to stall or quit. It occurs after running about 10 minutes and especially when in high gear pushing snow. The engine will go from sounding strong to muffled and slow.

At that point if I don't play with the throttle and put it in neutral it will usually die. Sometimes it will backfire and/or spit a lot of black smoke out the exhaust. Every time I pull the plug it is black & oily. Once this happens once it tends to happen over & over again until I let it sit a while.

So far I have:
Replaced points & condenser
Installed a new carburetor
Tried multiple spark plugs
Checked the spark (strong & blue)
Changed oil
Checked all the wiring
Messed with the carb adjustment screws more times than I care to
Added mystery oil to the gas

I've learned a lot about these engines but it's starting to get a bit frustrating. Not sure what to do next. Any suggestions?

[bocephus1991]

Did it do this before all the new parts? Did you check fuel flow from the tank? Do you have a fuel filter on it? Could be a fuel problem, I wonder if it ain't carbon build up on the head hitting the valves? I'd check fuel flow first then double check your adjustments on the carb. If no ones ever been in that engine I'd say it's carbon build up. Once it gets hot it's putting the Valves in a bind. I'm sure Jon and Don have better advice, they should be along to comment soon.

[raytasch]

Have you considered carburetor icing as a possibility?

[J-Mech]

Wow, you replaced a lot of parts! Hope you saved the old carb.

It's a sticking exhaust valve.

Need to pull the head, take the valves out, de-carbon everything, plane the head, clean the valves and guides, and put it back together. Valve job would be in order too if it was my machine.

If you question my diagnosis, you can confirm by getting it to act up, then taking it inside, pulling the plug and using a blow gun (with a rubber tip) on an air compressor to put a little pressure in the cylinder through the plug hole. You should hear air coming out the exhaust even if you roll the motor.

Note: DO NOT roll the engine by hand while putting air pressure in the cylinder. It may turn on it's own, and hurt you. Stop the air to roll the engine.

[red211]

With my limited cub time I have not had the valve issue yet. I have had the coil thing and this sounds like it could be that too. I know you said it has good spark but that is always a little iffy grounding a plug and looking at it. I am sure it needs a carbon clean either way so pulling the head is never a bad move. I like the run it till it acts up and put the air too it. If no leaks start it right back up and see if it still act up. Don't rule out a coil if it passes air test. I would sure do some more dio before throwing any more parts at it. J-Mech has forgot more about these things than I will ever know so a good air test is in your future.

[johns cubs]

If plug is oil soaked it could be rings, or valve seals.

[J-Mech]

Originally Posted by red211

I know you said it has good spark but that is always a little iffy grounding a plug and looking at it.

Really? I think that's a pretty good test.
If he is getting a nice blue spark..... I think we can rule out that the plug isn't getting grounded good. Plus, if the coil was failing, I doubt he would get a nice spark even when the coil was cold.

Originally Posted by johns cubs

If plug is oil soaked it could be rings, or valve seals.

Oil on the plug can also be caused by low compression due to a stuck valve.
K series Kohlers don't have valve seals.

[red211]

[QUOTE=J-Mech;315810]Really? I think that's a pretty good test.
If he is getting a nice blue spark..... I think we can rule out that the plug isn't getting grounded good. Plus, if the coil was failing, I doubt he would get a nice spark even when the coil was cold.


This could very well be true, you have worked on more of these than I will ever see. I do know sometimes you can get a spark when the plug is pulled but under compression it won't jump. A nice blue spark could but a good spark to some is not much to others. I know I chased a coil for a while and run for a while, run like crap, idle but not throttle up, come back for a minute and then fall off, die and restart after a few minutes and run fine are all signs I had. I chased fuel for a long time since every time I pulled bowl it would have a little rust in it so I just kept thinking fuel. I was lucky the motor was good since a coil is real easy to fix. Not that pulling a head is hard, just takes longer than bolting on a coil. Coils aren't cheap so I would test before throwing stuff at it and see what sticks.

[J-Mech]

Originally Posted by red211

I do know sometimes you can get a spark when the plug is pulled but under compression it won't jump.

Compression has no effect on spark.

[j4c11]

Here's a link to everything anyone might want to know about the theory of spark plug discharge and the factors affecting the voltage needed to obtain a discharge.

http://naca.central.cranfield.ac.uk/...report-202.pdf