I would be sure that the fuel pump is continuing to run when it starts. It gets a signal from a crank sensor. Without this signal I believe it starts and then quickly dies. Or even better as suggested rule out the fuel pump by removing fuel pump relay and bridging the neccesary terminals.
Am I right to think you can increase the pressure to the injectors by pushing down the flap in the air intake? So if someone will turn the key for you, you may be able to use this method to keep the motor running, instead of pouring fuel in the intake. It may be possible to rule out clogged injectors etc this way or at least get a better idea how things are going?
Oh in case you didn't know how this Jetronic system works - interesting:
http://www.youtube.com/watch?v=WFhJLLCjKdQ
that's so cool!
good luck