I have an urban express... it pulls great and runs fine until the very top of the throttle, and then it starts four stroking.
The odd thing is, the plug looks great and tan. I'm running a stock jet and even with no air filter and the mixture screw as lean as it will go (almost), it seems to run exactly the same and four stroke at exactly the same point in the throttle as when I have the filter on and the screw as rich as it will go.
Is there something else that can cause four stroking-like sounds, or is there something that can cause it to run so rich that a lack of filter and lean screw wouldn't make much of a difference?
Thank you everyone