My piaggio zip 70cc 2 stroke turns on then dies, it was ideling yestaday and running fine but bogging when riding, I decided to look at the mixture screw and idel screw and changed them a bit I think that may be why it keeps dying after starting, I have a 90 jet with a open air filter on a 21mm carb so I also feel as though I'm running too low jet I have got a 102 which i feel will be better but hasn't been fitted yet, any ideas what could be the problem ?