Has anyone experienced problems in very hot weather? My exmark with a 21 hp kawasaki will start and run great until I turn it off after mowing several homes. After it sits in my enclosed trailer to be moved to the next job site and is restarted it will almost stall or will run erratically,then it smooths out and will run fine. The carb was disassembled and was clean,no water in the fuel,and the cooling fins are clean. Recently it now does this first thing in the morning when the engine has only run for one minute and isn't even hot. Any ideas?