Check the coils. Sputtering at times makes things sound like a fuel issue when in fact its the first sign of Electrical issue. Now days with the Ethanol fuels and especially on a mowing machine the engine temps run hotter than normal sometimes simply due to too much grass clippings plugging the air supply for cooling and of course ethanol mixed fuels run hotter due to the fact fixed jet carbs are jetted for gasoline not a Ethanol blend. All this add up to heat, heat kills electrical components. Do a check on the coils to start.