Well my guess is that your throttle cable ha streched a little and is activating the saftey cutoff switch , its a little pin switch behind the throttle lever , on the throttle assembly . What you have to do is adjust the throtle cables by turning the adjuster nuts on the tops of the carbs . Just make sure you do the same to all the carbs , also you shouldnt have to go out that far so do a little then try it out and see . If you go to far you might un sync your carbs ....