Thanks opjose,

The engine is a SC (Super Custom) 46, 2 stroke.

I dont think its the spring in the carb, the aircraft flies on its side and performs fast axial rolls without hickup.

My thoughts are definitely towards your other two points. I've inspected the tank and tubing and honestly cannot see where a restiction (pinch) might occur during high 'G'. So the only other possibility is the weight of fuel issue during high 'G'. I've inspected the muffler and pressure line and can't see any problem there either.

Could it be the engine in any way as opposed to the fuel issue?