Yes, you can rotate backwards if you're not careful.
In the case of a Hilborn, remove the inlet fitting from the metering valve block and look down into it. Now notice that the inlet hole in the top of the block is not centered. One side is wider than the other. When the spool rotates open, the slot MUST open up on the narrow side, NOT the wide side. The hole for the secondary must be visible in the idle position and disappear to the WIDE side upon throttle opening.
Metering valves are made in each rotation direction, but spools are able to do both directions (just turn it over 180 degrees). If your metering valve is the wrong way for you, you can turn it around (secondary fitting facing backwards) or put the arm on so that it pulls from the bottom to change the direction. OR...set your butterflies up to open the other direction.
Spud