my yard machine i bought last year have used it twice no problems.started to use it today but after a while it shutt off with a back fire and a cloud of white smoke then it stalled.tryed to restart but no go.had to recharge batt tryed so many times. i changed the plug put in new gas changed oil still no start checked to see if getting spark and it great cranks realy good but no starting sprayed staring fluid in carb but still no start its a 16.5 500 cc B&S OHV power built model # 13AN775S000 help