Posted May 25, 2014 - 08:34 AM
Hello and welcome to GTTalk
Those engine do have a propensity or head gasket loss. I was told the Kohler engines added a head bolt to later series.
Change the oil with synthetic. It handles heat better and there may just be enough sludge in there to cause issues when hot. If you do a cleaning additive, make sure you do another change after a few hours run time.
Some other things to look at.
Runs fine until it gets hot could be many things. First things to look at is under the engine tins. Make sure it's all cleaned out under there... A hot engine can have some very bad issues, including valves sticking and the magneto failing when hot.
Next, change the fuel filter. Even if it looks ok. They will cause very weird problems. I keep forgetting this, and smack myself later.
If its a hydro, check to make sure the gas line isn't laying on the rear end. The hydro's put off a lot of heat and can actually cause the gas to boil in the fuel line.
Lastly, I would change the air filter. I am fairly certain it isn't that, but it's a good idea anyways.
Odds are, if it isn't this kind of stuff, it's either a Mag that has broken down to far and acts up from heat or its an internal issue