I replaced my stock 2 pump system on the Shelby Charger with a Walbro 255. I was running about 40 psi or so with +20s (vacuum disconnected). I could not get the car to idle (kept stalling) in open loop until the O2 gauge warmed up with 40PSI on the Walbro pump. I cranked the pressure up to 55 PSI and it seems much better and will idle. Why would I need to run that much pressure on +20s on the Walbro pump when the stock dual pump could run on 40 PSI?