remove sparkplug and re-fit it into plug cap and rest the plug on a metal part of engine to earth it, crank engine over with ignition on to see if there's a good spark, if you've got a spark then you need to check that you have enough petrol in tank and is getting to carb, remove pipe from carb some petrol should come out, you have a spark & fuel engine should fire up.
Jimmy
March 2012