You need to use an accurate gage or at least one that someone else has used and verified to be accurate. Its not uncommon for you standard gages from the parts store to be off a couple pounds. I used a certified test gage from an industrial facility to get my baseline then bought a cheaper glycerine filled gage (to dampen the pulses) to make all my adjustments with. Once I knew the fuel pressure was exactly 45 psi with the test gage, I knew that when my cheap gage read 44 lbs it was actually 45. I then adjusted my pressure down to 41 psi, knowing that it was still within factory spec at 42 psi.
All you need a length of rubber fuel line some hose barbs and a tee. Just remove the fuel line from the fitting on the front of tank and plumb in your new line with a tee, some barbs, and a gage. No need to cut the factory line if you just doing a temporary install to check your pressure.
For a permanent install BDX makes a really nice fitting that replaces the fitting on the front of you fuel tank. Just make sure you fuel level is below the fitting before you install it. Its about 18 dollars IIRC, then you just need to come up with a gage. Try to find one that goes from 0-80 or 0-100 as most gages are the most accurate in the middle of their range.
