Has anyone had a fueling issue after installing a larger fuel pump; namely the car going way lean after about 6K RPM with only a quarter tank or less; a half tank or more it works fine during a short WOT run?
I recently installed a Walbro 255L pump, in my 05 Cobalt; The stock pump has two strainers, one on the canister/module and the other on the pump itself. The only thing I can think of is that either the pump is sucking so much fuel that the canister can't fill back up fast enough and when it is half full or more there's enough fuel for a short WOT run. Either that or the pump isn't sitting vertical in the pump assembly.
So I wonder if anyone else has had a similar issue and what was the solution?

 

From other sources it sounds like the Walbro 255L fuel doesn't have a venturi tube for filling up the canister; so the next question is has anyone modified one of these with such a tube?

 

Well according to "the book" the venturi pump is loacated at the bottom of the fuel pump assembly and not on the fuel pump itself, so I have to assume it is driven by the return fuel; so perhaps it's restricted somewhere.
Has anyone seen this happen before?