[Aussie Mike]

The only clue here for me is the long sweeping corner so I'll take a couple of guesses. You may be experiencing fuel starvation as the fuel is pushed to one side of the tank exposing the pick up. Does it do it on the straights as well?

When you are under WOT you are probably sloshing the fuel around more so the pick up has a chance to catch some fuel.

If it get's worse the more laps you run, maybe the fuel level dropping every lap means less fuel around the pick up? Does it happen when you have a full tank?

A sump in bottom of your fuel tank for the pick would probably help.

I may be wrong here but it shouldn't be to hard to prove either way.

Cheers