The rear bearings broke and i heard you can just weld it together... is that true. Also not much power or acceleration on the xg550. What am i doing wrong.

just order a new set of bearings from X-Treme Scooters | XG-550 Gas Scooter Replacement Parts
as for the power and acceleration, do your tires have at least 40psi in them?
have you tuned your carb?
the xg is solid scooter but it needs weekly maintenance if you plan to ride it everyday