Have a 2003 Tiger Cub STC48A-19K with FH601V Kawasaki engine. It has 1200 hours and has been a reliable mower. This fall while mulching leaves, have had sputtering issues under heavy leaf loads. This sputtering happened earlier this summer which was corrected by replacing the fuel filter. Replaced F/F again, checked under deck for clogging, ok, but sputtering continues. Found out it does this when fuel shut off valve is in the right tank position. Put on left tank position and sputtering ceases. Could the right tank extra fuel line length or perhaps fuel tank gunk be at fault? My next task will be to remove right fuel tank and flush it out as well as fuel lines. Any opinions? Could this be more than just fuel issues or am I on the right track?