Ok, I have an 85 GSL. The problem I'm having is that it will start, but will not stay running unless the choke is out or I'm giving it gas. Sounds like a vaccuum problem to me, but I'm new to these motors and wouldn't know where to start.
I'll include a pic of the motor if it helps.
Thank you in advance. I really would appreciate any help you can offer.

 

If you can get someone to help you keep it running, many vacuum leaks can be narrowed down by the whistling/sucking noise they often make. Using a cardboard tube to focus your hearing on a small area (kind of like a stethoscope) can help a lot.

Careful visual inspection, looking for hoses or vacuum connections that don't have someplace to go, is also important.

Main culprit tends to be the question-mark shaped hose that connectes the brake booster hard line to the manifold; they get heat damaged over time, and crack underneath where it's hard to see.