Carburetor Leaning out on Long left hand sweeper

[Curt C.]

I am experiencing a lean condition on a long left hand sweeping turn at my local road race track (Spring Mountain in Nevada). Carb is 775 Race Demon running on a 408W. I am running dual power valves with spring loaded needle & seats. Road race floats. Fuel pump is an in tank 255lph. I don’t think it is a pump issue as the fuel pressure (at regulator) shows good at 6.5psi. It does it when the tank is full too. When I go around that turn I basically just keep the engine at 3700 - 4000 rpm or so in 3rd gear at part throttle as I am at the limit of mechanical grip. I can feel the engine slowly lean and have confirmed it with an AFR monitor – 15:1. Once I get on the straight the AFR comes back down to normal under WOT – 12.5:1. What is going on here? The fuel feeds from the passenger side of the carb. Is the G-force resulting in lack of fuel? Or is it that with two power valves I don’t have enough “jet” to run the engine at that sustained RPM with the primary bowl only?