This Aeromotive pressure regulator thing is turning out to
 be a real can of worms. With the MSD roller pump screwing
 the adjustment PR screw all the way in had near zero effect.
 In other words the pump was still overpowering the pressure
 regulator to the tune of 70 psi fuel pressure. Either the spring rate
 was too low or the body of the pressure regulator too
 large (area of the diaphragm) for this pump. I sealed the
 vacuum side well enough to get the vacuum down to 5 inches
 of Hg absolute. It was still leaking vacuum but it took 30
 seconds or so to leak down. Of course it had no effect on
 the fuel pressure as the PR spring was bottomed out.

 I hope they are not all like this. Probably the best thing
 to do is use the stock pump with the stock regulator
 as Mazda probably has all this stuff sorted out.
 That means of course the pump must be in the tank.

 The MSD pump has a maximum pressure rating
 of 95 psi. I had to turn the voltage down to 5 volts on the pump
 to drop the pressure down to 30 psi. One of the nice
 things about it is the over pressure bypass is internal
 to the pump so it does not spit fuel out when the
 output is blocked unlike the Walbro type pumps.
 The MSD pump can be used stand alone outside the tank
 unlike the vast majority of in-the-tank Walbro type
 pumps. One of the other features is it does not have a
 one way valve on the output. When you shut the pump
 down the fuel pressure leaks down back through the pump.
 That can be good or bad depending on how you look at
 it. If not good a external one way valve can be used.

 I can see why Ford went to PWM pumps. I can also see why
 carbs are still popular in certain forms of car racing :)

 Paul Lamar


Can I see a pic of your plumbing hookup

Skip Gorman

You hit the nail on the head. It is incorrect.

I have to go to the hardware store now and get parts to fix it.

Paul Lamar