I've had pretty good luck by initially setting it with the shroud off and engine not running (of course) by adjusting spring tension so the spring can just barely move the vane all the way open, then maybe one click harder to the wide open stop. Move the vane with your finger to various spots and make sure the spring can still move it all the way wide open. If it doesn't have enough reverse tension to move it wide open, give a click until it can (this will not be very many clicks unless you assembled it wrong). With this light preset, any engine speed will reduce the throttle (so it won't run wide open when you start it) and you'll have maximum range of movement. You can then tighten it further to increase engine speed.
It's a pain to adjust it after it's all back together, and dangerous to do it while it's running, so getting it as close as you can before you put the shroud back on is worth the effort.
