Carb issues???

[Madman752001]

Hello, I have a 05 UM X-Speed 50 scooter with the 50cc Minerelli engine. Just recently installed Scooter Parts Express 70cc BBK kit. Also installed aftermarket exhaust and removed the stock air box and replaced with "open" air filter. Scooter started right up with a little tuning and sounds great on the stand. It revs up beautifully on the stand, the problem I'm having is of the stand it has no power and stumbles off idle all the way to full throttle and will die if you don't release throttle. I went thru the Mikuni carb and put a "90" jet in it and the air mixture screw is at 1 3/4 turns out to get best idle. It starts and idles beautiful but won't run down the road. Any help/ideas would be appreciated. Thanks