i havn't checked the pressure at the back of the TBI unit.
i assumed since the pressure in the tank is causing a suction in the tank it must be sucking hard enuf
i have been running it around with the cap loose and it seems to go ok i just filled it to the top and now i have figured that when it starts to dip below the F mark its time to feed it another 100
the book says the pressure should be 14-15 psi with regulator vacuum hose attached and 18-20 with it disconnected.
i dont have the tool needed to do this test.