First things first.whenever I have to work on any 2stroke machine that has a problem. Remove exhaust and see if piston is scored,looking through exhaust port. A scored piston and rings depending on severity,will still start and run .but due to incomplete burn ,due to blow by will fowl plug . If all good,as stated previously check air filter.Those G4 carbies can take 2 different sized fuel needles.black and yellow .Black is shorter than yellow and therefore will raise fuel level in float chamber. I have never ever seen,in all my years as a small engine mechanic specialist ,working only on outdoor power equipment.a lean running engine produce a black plug.In that case they are grey/white looking.
