Back to working on my XJS in hopes to get it all sorted and back on the road for spring. Deleted the old vacuum advance timer system which greatly improved things. Still a minor hesitation when applying throttle so I decided to check for vacuum leaks.

It seems my over-run valves at the front of the intake manifolds are letting just a slight amount of vacuum through at idle, which means the spring has probably gotten weak over time from what I've been reading?

The bolt that goes through the spring, does it need to be tightened (and compress the spring) or loosened (to relax the spring) to block more airflow at idle?

 

My take from way down here.

Tighten that nut is the way.

My resolve was to remove them on all my V12's.

Jaguar fitted them, removed them, fitted them, throughout the range.

That removal, and a simple alloy plate I made to blank them, sharpened them up significantly.

All that dumb pollution stuff, we had very little, hit the trash can also.

 

I agree, I will end up deleting them at some point. Might look around and see if anyone sells the blanking plates, or maybe I could make up something inside of the existing housing.

I ended up figuring out on my own that tightening the spring was the correct answer. Had to take them in an out a couple of times because they didn't seem to be sealing for some reason, but that seems to be fixed now, I can't feel any vacuum being pulled at idle.

Still have a strange surging idle and throttle hesitation, probably a vacuum leak I haven't found as of yet.