F3G,. .. .I'm not current on the Pup but I used to instruct on the RAF Bulldog and I think the fuel systems as far as the engine are probably similar, albeit the Bulldog having fuel injection as opposed to your carb. (Sounds like "trust me, I used to be a doctor!" <img border="0" title="" alt="[Smile]" src="smile.gif" /> ). .. .Firstly, fuel pressure is NOT an indication of quantity of fuel flow to your engine, in fact the fuel pump's job is only to pressurise the fuel lines to ensure a reliable supply to the carb. The carb has a float which shuts off the fuel to a level from where it is DRAWN out through the jets by engine manifold depression. (An injection system picks up fuel and re-pressurises it through the injectors). It is incorrect to think that your fuel pump/s act like a spraygun such that increased pressure means more fuel flow! (Otherwise your engine would go extremely rich when you select your electric pump on).. .. .The electric fuel pump IS there as a backup to the mechanically driven one, we used to use it near the ground (where we were unlilely to successfully bail out) and for aeros, stalls, spins, PFLs etc.. .. .The fact that you are able to see a difference in indicated fuel pressure with it selected on is a bonus, and if I remember correctly was part of the run-up checks on the Bullfrog. By observing that your normal fuel pressure increases with both pumps selected on, you then know that the electric one is working correctly, as opposed to a warning light which might only mean that the switch has been selected on.. .. .The bypass line in the system is there to ensure that one failed pump does not jeopardise the correct operation of the other.. .. .One thing I might want checked though is the normal fuel pressure capability of a fully serviceable mechanical pump. 2 psi sounds a little on the low side, I would have expected 3 psi. I suggest you just confirm this but it sounds like your system is otherwise quite normal.. .. .Hope this helps!. .. .Regards, ShyT. . . . <small>[ 04 March 2002, 23:36: Message edited by: ShyTorque ]</small>