It helps to get the fuel up to the pump, if you also close the little hole in the choke plate. Also it helps, if you supply a little pressure to the tank. (blow on the vent line)
This is a Walbro issue, not MVVS. Clean the carb well, and re-fit. Do not tighten the central cover bolt much, because that will cause the pump petal valves to curl up.

About tuning the carb, a lot of bed time stories are told as stuffing for the forae. I found,[link=http://www.prme.nl/forum/viewtopic.php?t=10] this way works best, and is quick to adjust[/link].