Hello All, I have a Kohler that is giving me problems. Its a CH22 twin cylinder horizontal shaft engine mounted in a Cub Cadet tractor with about 500 hours on it. It starts fine. After a few minutes of running it gets real weak. Just turning on the belly mower or aggressively climbing a steep hill bogs it down bad and almost kills it. I suspected that it was only running on one cylinder so I put it away in the garage to be looked at later. The next day I tested the spark at both cylinders. Tested fine. I checked compression and both cylinders also checked fine. Just for kicks, I checked the fuel supply. The hose coming out of the pump was running very strong. I gave the carb a quick cleaning and put it back on. I put it all back together and started to mow a little grass. It was running fine up until about ten minutes into it when it started to get weak again. I quick limped back to the garage and checked spark and compression. Both were fine. This time, I removed all of the front engine shrouds and heat shields along with the entire exhaust system. I fired up the engine and it ran fine (loud but fine). I felt with my hand, that the exhaust from each cylinder was hitting very strong signifying that each was firing strong. I took of mowing grass with the loud engine. This time, about five minutes into it, it started running weak and I could feel / hear that the left side cylinder had stopped hitting. Once in a while it would hit a couple of times, but for the most part, it was freeloading and not running. I removed the valve cover and pushed on the valves and they seemed ok. I'm stumped. I think its either a valve that gets hung up once the engine warms up or a bad spark that gets lazy when it gets hot. Does anyone have any experience like this? Which direction should I go? Advise?