Dont know if any help mate but i once put a new petrol tank on my S1 (aftermarket jobby)and the swirl pot in the tank was`nt right and was`nt supplying the pump with fuel when i went round a right hand bend, also on my 3dr sierra that had been parked up for years i took it out for a test drive and this did the same thing cutting out round corners but the swirl pot had actualy rotted of in the tank. like i say mate you`rs might not be the same prob but worth a try.