have you drained out the fuel and topped it up with fresh fuel? todays fuel only has a shelf life of 28 days before going off, {if don't beleive me contact shell and ask them].if this dose not work remove the cowl and flywheel and you will find and aluminium cover, undo the 2 1/4" screws and you will find the points make shore there clean and not burn't, but if you go this far a new set probably is not a bad idea and a new plug, set the points to about 0.018" good luck.
