My kohler 4ckm21 generator starts great but will run for 8 min. and shut down ?

SOURCE: kohler 12kw generator starts but shuts down after 3sec

Your gas pressure is too low and you may not have a large enough supply pipe. You need at least 10 inches of water column with the engine running to operate an LP vapor fueled engine. Because the engine is starving for fuel, its governor opens the throttle to WOT (so it goes to high revs) but there isn't any fuel to make horsepower with so the output voltage falls and the undervoltage alarm trips.

Carl

SOURCE: kohler confidant 4 generator service manual and wiring diagram

First thing is to check oil level as low oil pressure will shut it down.

SOURCE: kohler lp shuts down

What you need to know is there enough fuel going to the regulator. It should be 7 to 11 inches Water Column. If not your problem may be not enough fuel. That includes when the heater in your house kicks on and what ever gas appliance you may have. Once you verify that you need to figure out if you have the proper pressure coming out of the regular on the inside of the generator. Next I would look at compression of the cylinders. It may need new piston rings.

SOURCE: kohler generator drains battery while running and

The rpm sensing in the control module is missing or bad.
Answer these questions for more details:

1. Does your generator output normal voltage?
2. Is the starter turning after the Gen is running?
3. Is the charging of the battery connected?

SOURCE: 4ckm21 generator runs only if

I had same problem and to make a long story short, it wasn't any common problems like oil pressure switch, etc. Solution was the start stop coil/ ignition coil. Looks like a 1" ice cube behind the panel and it usually (not always) has a tattle tail indicating failure.