At forty years of age no fuel system is reliable, or in perfect condition. Given the strange complexities of the D-jet system it's a system for purists only at this point.
I began working on D-jet on VW, Mercedes and Volvo in the early 80's. Even then they were giving trouble. Ten years after that, and wiring faults, locked-up fuel pumps, blown pressure regulators, worn out trigger points, leaking injector hoses, worn throttle switches, AAV's that wouldn't slow down....you name it. I've also seen lots of burned up 140's and 160's from fuel fires....fortunately never to one of my customers - but close a few times....
So as the D-jet stuff is really expensive, and throwing new parts at a collection of used bits that aren't truly acting as they should.....one wonders.
Carbs are the answer. Not better in and of themselves, but the answer.