Agree with Tony on this but would also take the carb off and apart for a good cleaning / inspection. There is not a lot to them. Guessing that you are using a good quality fuel filter and that the tank and likes were sanitary ? We use a ultrasonic cleaner on carbs after every outing to ensure that they are clean and remain clean. Not to mention the fact that pump fuel can often lead to problems.. If you continue to have problems, give us a shout..