When you change the airbox out for a open filter, you must lower your popoff pressure to compensate. Keihin makes 3 different springs that I'm aware of. You'll need a small air pump to test it. I'm not sure what stock popoff pressure is on a keihin but try to get the popoff around 20-25psi and see what that does. That should allow more fuel sooner. When you change the filters that are less restrictive, you weaken the vacuum signal that pulls the fuel through the needle and seat therfore changing the spring to a weaker one will lower the popoff