Look around the throttle wheel, there is a stop screw for full open. The slides should stick into the throat of the throttle that much, adjusted with that stop screw. The back side of the slide, not the cutaway edge.
I don't know offhand which screw it is, that should be obvious when you turn the wheel all the way open.
This isn't a super critical adjustment. Usually only needed if you completely disassemble the card rack and have to start from scratch with adjustment. There are several other adjustments needed if you've done that in order to get the idle screw and choke throttle advance working properly.