Try this, and if it doesn't work, get back to me.
On the linkage side of the carb, at the top of the carb body, there is an arm with several holes, a retaining screw, and an "S"-shaped connecting link to the pump itself. This is the accelerator pump arm. There is a linkage rod fit into one of these holes and retained with a tiny cotter pin.
Since you're coping with altitude, you want to have this adjusted to the quickest response, which means putting the linkage into the hole CLOSEST to the retainer screw -- the innermost hole which will create the quickest reaction for any given throttle change. In contrast, placing the linkage rod into the hole at the end of the arm, farthest away from the retaining screw, will slow accelerator pump reaction time.