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.