I do it a little differently since the Walbro carbs do not have a mid range needle.

I set the idle up to about 2500-3000 rpm. The prop size has no relevance. Tweak the low needle to attain the maximum rpm possible at that idle setting. Now go to the high needle after running the engine up to max rpm. Peak the high needle to max rpm, then past just enough to hear the rpm start to fall off. Back off the needle to the rich side to just short of the peak rpm. Check the low to high and back transition. If it's good, then go fly and make minor needle adjustments as the engine breaks in. After it's broken in you may need to adjust the needles avery 6 months or so, or if you make some changes in flying sites that vary more than 1,200 feet (+/-) in elevation.