Take the carb off for a really good clean, using an aerosol carb cleaner. Look for water or any debris in the float bowl. Treat things very carefully - you don't want to bend or adjust either the float needle valve or the throttle slide needle. At the same time, check for fuel flow from the petrol tap and through the filter. If there is a pilot screw on the side of the carb, set it at 1 1/8th turn out from fully in.
John
May 2009