I cant see that its going to be anything else, if you have changed the metering head for a known working expamle, unless you are really unlucky and it failed as soon as you fitted it, all should be OK.
Your fuel in ( from filter) is good, and you have good fuel return, it only really leaves the warm up regulater.

here is a website that gives a reasonble detailed overview of the K-jetronic system.
http://www.auto-solve.com/mech_inj.htm#top