took the 470 out to a track on the weekend ,everthing was ok bumped it first time ran then stopped suddenly so started it again and it ran for 10 seconds then stopped so i changed plug checked for any loose wires put it all back together it started ran for a few seconds then stopped , checked plug and it looked wet like it was getting fuel so had a friend tow me round a field and same started ran for a few seconds then stopped . were do i start ?