hi, all. my mechanic recently sold me, very cheap! a weber downdraft to replace the anemic single zs carb on our 75 sptifire. herebs a picture of it: www.ranteer.com/misc it seems to us that at full throttle the butterflies should be open, not closed. when you pull on what we think is the accererator, it close the butterflies, not opens them. what am I missing? thanks!