its one of my customers mowers it 4-6yrs old but probobly only has about 20hrs on it total and its not been used in a year but it starts easy on the 1st pull, so far ive drained the old gas and filled with fresh ive also taken the carb apart and cleaned it but it was already clean it starts right up on the first pull it has a blade clutch that you have to engage "lightly" so the engine doesnt die this could also be part of the problem but once you get it engaged and start mowing its fine for about 20 sec then it sputters and dies and also backfires enough to blow the airfilter and cover about 2 feet from the mower ive also tryed lossening the gas cap incase it was clogged but it didnt help when i took the flowt bowl off whith the fuel line still hooked up it pored threw the carb fast and the flowt shut it off fine also it always starts right back up and runs for another few seconds then repeat any suggestions would be good ive never come across this problem where i cant fix it i guess it could also be electrical related