I have been depending on a cheap 15 psi fuel pressure guage and regulator along with my mallory comp 70 pump. Well the cheap regulator crapped out on me so I set the pressure using the regulator that is built in on the Pump. Well I finally spent some money on a very good 1-5 psi gauge from McMaster-Car and temporilarily mounted it to check my setting. I learned two lessons. First the cheap gauge was WAY off, I thought I was running about 3psi and was running 5+!!! Also I did a test drive and found that the pressure would fluctuate wildly depending on whether I was accelerating or decelerating. I could slam on the brakes and the pressure would shoot way up past 5psi!!!!!! I deduced this was caused by the fact that the regulator was on the pump at the rear of the car and the inertia of the gas in the line contributed the pressure fluctuation. I got a good Holley regulator (1-4 psi), installed it very near the carb (Mikuni 44 pph), adjusted it to 3.5 psi, turned the regulator on the pump all the way up and now my pressure is rock steady and does not fluctuate hardly any (less than .2 psi!!!)
This makes my car run soooooo much better than before, I now fully appreciate the importance of correct pressure, I should have never tried to get by with cheap stuff.