Was wondering if someone could help me with my kohler 14 engine. It is 3 years old, and is in good mechanical shape. It backfires when it is under a load. Bad. I have put in new gas/filter/plug. Have tried to adjust the idle adj. screw, but still no luck.The exaust smells very rich. Could there be a problem with the float or possibly the ignition moduel or valves. Please help.