I have a kawasaki 21hp twin cylinder engine that is having problems now at less than 100 hours. It runs ok, but feels a little weak initially, then loses more power after about an hour of use, until it eventually starts dying completely when you put any load on it at all. It will immediately restart, but is very weak. Dealer has replaced carb assembly but it still has the same problem. Any ideas I could pass on to help my dealer solve the problem? Searching the web, I came up with things like carbon buildup on the coil (resistance increases as it gets hotter) or valves not closing completely as the valve stem elongates slighty as it heats up and expands. Anyone else out there have a similar problem they were able to solve?