I am restoring an xr4i 2.8 v6 for a friend that has been standing.
I am having problems getting the car to run properly.I have fitted
a new fuel pump as the old one would only work with a knock and
a replacement metering head unit.
I can get the car to run if it is cranked over whilst i hold up the vacuum
chamber disc in the metering head unit but it dies as soon as i let go of
it.My question is what provides the initial vacuum to open the chamber
which then allows the fuel to flow through the metering head unit?
Any possible common faults causing this fault?

Cheers