OK, I've been trying to just watch this thread and not get involved, ain't working. For one, not all installations allow for the engine to be mounted in just any position. Remember some planes have cowls and such that the OP might not want to cut up. Some airplanes won't work with any tank position except the stock one, unless you are willing to do extensive modifications. In some applications the flyer might want his tank in a particular location to allow for a certain type of flying to work better. I am referring to 3D in this instance and the tank in my AeroWorks Extra 260 is back on the CG which leaves a long way for my 91 Saito to pull fuel while in a hover and the throttle is being pumped in order to maintain control. Frankly it won't do it; I have to run a pump. In my case I chose a VP-20 and after some considerable effort finally got it adjusted and wouldn't go back to unpumped for all the tea in....well we all know how that story ends. My point is with my tank some 10 to 11" behind the carb fuel draw was marginal when trying to hover so I went the pump route. Yes I could have moved the tank right up behind the engine and it would have ran OK, I know this because I have owned this particular engine for over ten years and it has been on numerous planes. It ran great on all of them. I now have the desire, which I understand some folks wouldn't agree with because it's not their idea of flying, to master the art of 3D. The smaller birds just work out better with the tank back on the CG mainly because the CG is set up right on the neutral point and the fuel burn would cause it to move too far aft making the plane harder to control.

Now that we have established that there are legitimate needs to have fuel tanks in unusual locations and that engines must sometimes be mounted a certain way the next thing we need is help getting the OP set up with his pump. On mine, I set the needles without the pump and then hooked up the pump up. My engine was running just a little too rich at that point and would die when throttled up so I started turning the hex inward lowering the volume on the pump until the tune was good again on the high side. In my particular case I had to lean the low end just a tad at this point. I can now fly an entire tank without the mixture changing any noticeable amount and can hover for the full tank if desired. That's with the tank a full ten to eleven inches lower than my engine while in the hovering attitude. It takes some effort to get everything set up right with a pump but IMHO and at least in my case it is worth every minute of it.

For the OP, don't give up, the VP-20 can be made to work nicely on a four stoke.