I have a walker with 25hp kohler, 1,600 hrs. The head gasket replaced about 10 hrs ago and the valves lapped. It starts fine cold and seems to have great power. Somethimes however, it will bog down while you are mowing like the choke has been engaged. The blades slow. Sunday I found some water in the fuel filter, so I drained the tank and replaced the filter. I checked the carb bowl and it had some trash, but no water. I cleaned out the trash and then ran it. It seemed to run fine. Yesterday a worker used it again and it started bogging down again, but it comes and goes. He mentioned that it often started when he turned up hill. The engine doesn't sputter, it just bogs down. Could there be a drop or two of water in the carburetor jets. I checked and the fuel filter doesn't have any drops of water now.