fuelling problems with uprated pump

[p fandango]

i can't get my head round this so hoping someone can make sense of it for me. BT's running a twin fuel pump system with a 2litre swirlpot. The factory pump fills the swirl pot, then the external 300lph pumps from that to the engine. Both pumps are hardwired & independently switched.

with just the factory pump on she idles perfectly, but won't rev when you touch the throttle. Yet when you turn on the second (external) pump she revs happily but over-fuels very badly on idle. The injectors are standard oranges, & the fuel pressure regulator is the original so thought should be dumping any unwanted fuel back to the swirlpot

any ideas?

[Jamest5r]

If you get the tt in there you could trim the fuel on idle with both pumps running.

[p fandango]

If you get the tt in there you could trim the fuel on idle with both pumps running.
oh yeh, i've got VXR injectors & 3.8bar FPR ready to go on once i get a TT. Just can't figure out whats happening now

[t5 pete]

With two pumps running it must be sucking too much have to tryed to swap the pumps around and see how the car runs just on the updated pump

[p fandango]

With two pumps running it must be sucking too much have to tryed to swap the pumps around and see how the car runs just on the updated pump
with just the second pump running its exactly the same until the swirl pot empties