I agree with Bogie's answer. Running 10 psi fuel pressure is just a tiny band-aid on your set-up, and will not make up for the lack of volume - volume being way more important. Now that the motor is ingesting more air (because you freed up the exhaust), the fuel demand is beyond the pump's capability to provide it.
Think of it like this - you will get more water out of a 2" pipe at 20 psi than you will a 1/2" pipe at 50 psi.
Bogie is smack on with his answer.