Hi there,
With the new information you divulged concerning the carburation attempt, it seems the intake manifold must have been removed. I'm wondering if it was reinstalled correctly, proper gaskets installed, etc. Also, does this engine have an EGR valve? If so, is it sealing properly? If the cam timing is correct, you just about have to have a vacuum leak. When it's running, try removing the oil filler cap - does it immediately quit? If so, maybe you have a vacuum leak into the crankcase area from the intake manifold. Whatever it is, it has to be fairly obvious to get the huge reduction in vacuum that you have. Maybe you should take Stevebfl's advice and go to a real pro!

Regards,
Richard Wooldridge
'82 300D/4.3LV6