IS THERE ANYONE WHO HAS UPGRADED THERE JR50 MY SON HAS BEEN RIDING AN XR50 AND WANTS TO DROP THE TRAINING WHEELS, SO WE BOUGHT HIM A JR SO HE COULD REACH THE GROUND AND THERE IS NO POWER AT ALL (HE´S 37# AND 4YRS OLD),I HAVE AN FMF EXHAUST COMING & OPENED UP THE INTAKE,HAS ANYONE REJETTED, BOARED OUT THE CARB OR TRIED A BIGGER SPROCKET ? IF SO LET ME KNOW HOW IT WORKED AND WHERE YOU GOT THE PARTS FROM