This is something which will not be cured by putting the engine on it's side.

The fact that this occurs only during fast high G maneouvers tends to point to a minor plumbing or pressurization problem.

You MAY inadvertently cure the problem by revamping everything as you've indicated, but you'll be just as likely to do so if you pull out the tank and plumbing and redo it all too.

Try making these assumptions and work with them to cure the problem dealing with one or all may overcome the problem:

- The carb barrel may be moving sideways in the carb, changing the needle setting, particularly at mid to low throttle.
- The weight of the fuel in the lines during high G grows enough to overcome the pressure differential causing fuel starvation.
- Something may be pinching off the fuel flow, either in the tank or outside of it.

I've had the first one happen to me, where the spring in the carb barrel body was so weak that the fuel flow was cut off whenver the plane rolled quickly or if I flipped the plane on one side such as in a knife edge.

Stretching the spring a bit to put more tension on the barrel cured the problem.

BTW: What engine is it?