Cub Cadet 108. Kohler engine, sputters & quits when warm, will restart .
 

I'm at my wits end with this tractor. Ran fine up until about 2 weeks ago and then all of a sudden started acting up. Will run fine until it gets warm (about 20minutes or so) and the sputters, backfires, & quits. It will restart almost immediately and run for a few more minutes (about 5 or 10). It seems like the longer you let it set the longer it will run longer, based on the time you wait before restarting. First I replaced points, coil, & condenser. Points set at .020. Carburetor replacement was next. The plug seems to be really black, so I'm presuming it's not fuel. I'm obviously missing something here. HELP !!!! I forgot to mention, I also removed fuel tank and cleaned it out.

First, welcome to OCC........... :Welcome2:

Sounds like something getting hot and changing. First thing that comes to my mind is perhaps the Valves, especially the "exhaust" valve. You might want to check that before shot gunning the engine with anymore parts.

:bigthink:

Are you referring to adjustment ? Or maybe burned ? Compression ? Also it seems like the engine has developed a little vibration (forgot to mention that). I just also noticed there seems to be some oil residue where the cylinder head meets the block.

The oil residue at the head normally indicates a blown head gasket or loose head bolts.

Remove the blower cover and check for grass build up in the cooling fins.

Then as R Bedell said, check valves. Make sure it's making full travel, not staying open.

Thanks for the suggestions. I'll respond with outcome ! :>)

Keep in mind the exhaust valve is on ACR.... If working properly, the exhaust valve will be slightly open.

I presume you are referring to "compression release"?? They used that on the older engines ??

I was referring to the common issue of carbon deposits on the exhaust valve stem. When hot, it expands, and closes the clearance on the value guide bore.

Yes with 2 revolutions of the crankshaft you will get the exhaust valve to go full open full close then a tiny almost unnoticeable open and close as well. Get it full open and look in to see how pitted/ beat up the seat and valve face are.

Cub Cadet 108
 

Also when you have it apart inspecting the exhaust valve and seat, give the valve a wiggle. Too much wiggle is not good either. There is a lot of heat on these valves.

Well Folks, I checked the compression today and it was 90 lbs. cold. I may do a hot compression test tomorrow. I also noticed when it it was cranking there was a lot suction at the exhaust pipe when the intake stroke was happening. Couldn't tell if any blow by on the compression stroke. I have a "whistler" that I am going to try to determine if any is present on the compression stroke. Also with that kind of compression it's hard to believe there is an exhaust valve issue, but I realize the engine was cold and the problem doesn't start until the engine is hot. I'll keep you posted as I progress. Thanks to all that have made suggestions.

Add a dose of Marvel Mystery Oil to the gas and some to the crank case.
That just may help.
Or remove the valves, inspect and reface and clean the stems as needed.
You can check for proper ACR adjustment then as well.

Checked compression today and it was 90 lbs. cold. Will do a hot test tomorrow. 90 lbs. seems to be adequate, but the hot test should indicate a stuck valve problem because it only acts up when it's hot.

Update on K 241 Kohler in 108. Have the engine apart and found a lot of carbon build up on the intake valve. Also a "blue" spot on the stem of intake valve. I presume that would indicated the valve was sticking and maybe why the carburetor felt very warm to the touch (vapor lock)? Going to replace valves (lap them in), springs also. Are the valve guides supposed to be protruding a small amount into the valve chamber? They don't appear to be worn.