Yes, a mechanical fuel pump can change pressure as it ages. As the diaphragm gets older it can become stiff. This in turn causes higher pressure to be generated. I was having the same issue with a VW Beetle. The Beetle was having flooding problems, and the pressure was 4.6 psi when I checked it. A pressure of around 2.6 psi was the recommended pressure. After checking a few sites, I came across an article that gave that as a reason. I installed an after-market regulator and brought the pressure to 2.6 psi and the problem was solved.
