(anonymous contributor)

You can raise your fuel pressure by sqeezing the regulator "can" with
the spring in it. That tightens the spring, and raises the fuel
pressure.

 On older regulators with the hose barb fittings, you have to make a
little jig to hold the reg in place as you sqeeze it in a vise. The fuel
hose fitting must be protected, and the reg must be held by the flange
that runs around it's center.
 Find a short piece of exhaust tubing or water pipe that just slides
over the body of the reg. You'll have to cut a slot in the pipe to clear
the fuel line fitting that sticks out sideways. Once the slot is in the
pipe's side, slide the pipe over the reg body until it butts up against
the flange in the center of the reg. The pipe should be just long enough
to protect the fuel line fitting (hose barb) that sticks out of the
bottom of the reg.
 To protect the little vacuum line nipple that sicks out of the opposite
end, use a chromed socket from your socket set. Slip it over the nipple,
and center it on the reg. Select a socket that'll push down on the can
just outside of the center recess where the nipple comes out of the reg.
 Now take the entire assembly of the pipe, the reg, and the chromed
socket, and place it snug in the vise jaws. Keep that socket centered!
Close the vise approximately 1/8", and your pressure will jump up about
10 psi.
 If you want to set your new pressure exactly, hook a rubber tube from a
pressurized air tank to the side fuel fitting that's sticking out of
your homemade pipe/jig, add a gauge to the line with a tee, and SLOWLY
crack open the air tank valve. The pressure will rise to a point, then
begin leaking out of the reg, and will rise no more. You'll hear the air
hissing out, and the pressure will stay at the same point. That point
should be 55 psi before you squeeze the reg in the vise. Each turn of
the vise will raise the pressure right in front of your eyes, and you
can stop anywhere you'd like. Don't go too far, because you can't back
up!
 60 psi will make your injectors flow 4.5% more fuel. 65 psi will give
you almost 9% more fuel. 70 psi gives almost 13% more fuel.

 On newer regulators with O-rings instead of hose barbs, like on '89's,
You can just use sockets on both sides of the reg, and don't have
to make the homemade pipe/jig.
 An alternative to the vise is to stand the assembly on a hard surface,
and tap the top chromed socket with a hammer. Don't go wild with the
hammer!
 Remember that injectors can be damaged by pressures more than 75 psi
over boost, and that you must have a good enough pump & filter to keep
the pressure high under WOT. Having 65 psi over boost at 5 lbs of boost
is no good if you have only 50 psi over boost at 20 lbs of boost. The
pump's got to be healthy enough to STAY at 65 over boost at all boost
levels. A clean filter is a must.
 Just check your fuel pressure at WOT, under boost, to see if the
pressure remains the same amount over boost.