SORTED THE PROBLEM ON MY SONS BIKE . BY RUNNING ON 100 TO 1 PETROL OIL MIX . A B7ES PLUG .SET PETROL SCREW ON CARB TO 3 & 1/2 TURNS OUT. ALSO CUT AIRBOX AIR INTAKE HOLES TO MAKE ONE HOLE. REPACKED EXHAUST. THE BIKE IS A 2004 MODEL. THE BIKE HAS NOW DONE NINE TRIALS ON THE SAME PLUG. IT STARTS FIRST TIME HOT OR COLD TICKS OVER AND REVS PERFECT. I CAME TO THESE SETTINGS AFTER A LOT OF FRUSTRATION AND SPARKPLUGS. ABOUT FIFTEEN PLUGS IN TOTAL