see above post, an intro is essential if you are looking for positive responses, your problem appears to be a valve not seating or incorrect float seating, a good clean and blow through of the jets with compressed air would probable solve the non-seating valve issue but a good clean is well reccomended, from what i remember from a rpevious posts the carbs on this model may have plastic float bowl tangs which will not allow you to modify their height.
remove the float bowl and let us know what the condition is in the float bowl, otherwise th evalve and seat may be pitted or corroded