I have a walker mt with a 20hp Kohler engine. I bought it used from a homeowner with only 200hrs on it. I have only put 50 or so hrs on it between last season and know because it has always given me problems. My crew usually runs it, so most of my knowledge of the problems are second hand. Let e first give you a little history on it as it may help determine the problem. The first problem was oil getting mixed with the gas. It would blow white smoke out of the muffler. Put it in the shop and they fixed it. The next problem was with the charging system. Not sure how it works exactly but it would not hold a charge. I had to keep jumping it off at every yard. Put it in the shop and got that fixed, along with new plugs, fuel and air filters and oil change. That was just a few weeks ago. Last week the guys bring it in with yet another problem. They claim the oil light came. Upon checking the oil level it was low. I ran the mower myself last week and it seemed sluggish, like maybe it was only running on one cylinder. I pulled the plugs and sure enough the back one was hot and obviously working, however the front one was cool, showed very little ware except for a lot of build up in the electrode gap. I replaced the plug and ran it again. This time it ran fine except it was blowing white smoke. I figured it would burn off. I stopped and checked it was not coming from the muffler but instead the side of the engine. I figure that somehow the oil is getting out and getting on the hot engine and burning off. I replaced the valve cover (took one off an old engine) on the side I pulled the bad plug from and everything seemed fine. I sent the guys out and told them to get a couple quarts of oil. Halfway through the day they call me with more problems. Now it is low on oil again and shutting down when it gets hot. When they got back in I saw they had put a synthetic oil in the first time (10w30), I have never used a synthetic in this mower. Not sure what that will do. I am about to go check the oil and plugs again to see how they look. If anybody can help shed some light on my situation it would be much appreciated.