I think that maybe I have given the impression I am arguing that the walbro out flows the bosch. I was just stating what I have. I have no flow issues at this time. I have thought about either adding another walbro or simply putting one of the stock pumps back inline as a feed pump. I do need more flow to go any further and I need larger injectors also. Right now though I am ok.
The check valves do have one hole though if you look at the inside. I thought the same thing about the four holes but if you take the fitting out of the pump and look inside the end you will see what I am talking about.