how can i start my flymo lawnchief rl 400 ?

It suddenly stopped while running. Have cleaned the faces of the magnets and the magneto unit and am now getting a spark on the plug which was not there on first investigation.Have reset plug to 30 thou and poured some petrol into air intake for initial try but still won't start. Could it be too weak a spark? faulty magneto unit? or is the problem no petrol[ however petrol jets out base of carb when the purge spring is depressed]. Help! any input you guys can offer would be gratefully received