How much line, and of what size, would I need to redo the entire vacuum system on a 1985 XJS?

 

Assuming you are referring to the ignition vac lines, this is what I did:

1. remove all of it, pipes, little solenoids etc etc and block off any unused ports to the manifold.
2. renew the vac capsule
3. run a single vac line from the underneath of the A bank throttle body (where there is an outlet correctly sized) to the vac capsule
4. disconnect the loom from the water temp switch on the A bank rear water manifold and insulate the ends and tie them off somewhere;

This will deactivate the 15 minute strat-up timer which just uses extra fuel to no purpose, and you will notice no adverse change in the cars performance. I was advised to do this by the Jaguar Enthusiasts Club guru, the great David Marks, and my car has been like this for years. Highly recommended


greg