Hi there I had the same problem with my son's py 90 all you have to do is locate the carb and you will find a recessed screw, turn it (sorry not sure which way) this will set up the bikes idle speed on tick over (do this when the bike is warm with the choke in) as when it is cold you will need to use the choke and it will throw out the tickover when hot. It may also be advisable to take off the top of the carb remove the needle sleve and spring carfully clean it out with carb cleaner and reasemble all this should not take more than 1 hr. hope this helps.
kids slave
January 2008