I have a Scag Turf Tiger that stalled while using it the other day and then it would start an run for a second and then stall immediately. I pushed it back in the garage and let is sit for a while and it started immediately and then stalled after one or two seconds. I changed the fuel filter-no help. I checked the operatio of the fuel pump-ok. Still no change. I pulled the carb apart , cleaned it (no visible debris or varnish) and still it strarts and stalls again. I thought about maybe the magneto was shorting out but it does not run long enough for it to heat up so I figure since it starts right up it must be ok. Any suggestions?