See where the throttle cable comes down, next to the domed part of the carby? Yea?
Okays, that should be connected to a little bracket with a nut on the side of it, and the cable on one end.. This is the throttle shaft. At the opposite end of the cable, there should be a screw (flat slot) which also has a hex-head. ie, not just a round screw. It will also have a spring wrapped around it. Turn this screw in (down) to increase revs, and anti-clockwise (out) to decrease
If the revs don't rise, you've probably turned the choke adjustment. Stop, and turn that back to where it was, and try the other one.
