Sounds silly but does the metering head flap move easily? if it has been standing for a long time this may have seized/stiffened up etc. The flap position correlates to how much fuel is injected.

Take an injector out next and look at what it does when the engine is cranked (unplug the cold start injector to avoid totally fludding whilst you are playing about), and when you push on the flap.

Let us know what happens

Rob,