Stock fuel pressure on gs-r?

Hey anyone know what a stock gs-r's fuel pressure's suppose to be. Mine was at about 42psi. But I'm having trouble with the a/f ratio. I don't have the money to take it and tune it on the dyno yet. So I was wondering what the stock pressure's suppose to be and go from there. I had the pressure at 46psi. I took the plugs out and they had white specks on them, so I raised it to about 48 - 49 psi. But then the car ran funny and would, what sounded like back firing....when I reved it. If anybody have a helms and can look it up for me, that'd be great. Oh and that's with the vacum tube in. Thanks.