I have a Bird Dog and have been double checking all the PS5C and fuel pressure info. The pressure should be the same with or without it on, pretty much. The manual say use it. If it makes it run rough, then the pressure is too high or the mixture is set wrong - or the diaphragm is about to fail and it will all go quiet. You can download the PS5C manual online and it is full of good info. For example, you must let the carb sit full of gas for 24 hours before it will operate properly, and you must check the mixture with the pump on. There are 2 mixture adjustments - for idle and cruise ops. They say the PS5C is sensitive to altitude and temperature changes, so if it got cold lately.... PS I operated 5 banner tow and Skywriting Bird Dogs out of Lawrence MA. Did you ever fly with us?