Can't help you with a diagram, sorry. When I got my 250C some of the vacuum lines were connected and some were not. After studying the situation and verifying that the various temp switches, relays and 2/3 way valves were not working either I just pulled all of them and plugged the vacuum source(s).

As far as I know there is no "kit" to fix the distributor so you will have to try to find a vacuum unit. The two inlets are as follows: The one pointing to the firewall is the advance port and the one pointing forward is the retard port. Original system w/all vacuum lines working used both the advance and retard sides at various engine speeds and conditions. Also was an early "smog controll" attempt.

When I ran by Zeniths I did NOT USE any vacuum advance I just set the timing at 10 degrees BTDC. The vacuum port(s) on the Zeniths (at least mine) are/were manifold vacuum and NOT s-port vacuum so there is/was full vacuum at the port at idle. S-port vacuum is applied as speed (hence airflow through the carb) increases which provides vacuum advance (I think). I do use the vacuum advance with the Webers but I still leave the timing at 10 degrees BTDC.

Double check for vacuum leaks and make sure that the vacuum pipes on the Zeniths are plugged at least while you trouble shoot the problems. Also, there is a hose (pipe) fitting with an orifice in the intake manifold between the carbs. This is the intake from the water/liquid separator at the bottom of the aircleaner. It is metered (has an orifice). Make sure that you still have the aluminum insert that the hose attaches to as that is what contains the orifice. If this is missing you will have a very lean and nasty engine.

As I stated before, after all the work I did I still had a hesitation problem that did not go away until I replaced my ignition with the Crane XR700. I had read on another list where an owner of another 250C had the same problem and had his distributor rebuilt and a new Bosch blue coil that solved his problems.

BWT: If you have any vacuum device that will not hold a vacuum (distributor, A/C solenoid, heater valve, etc) then, in effect, you have a vacuum leak and that will upset idle, transition, etc.

Hang in there....

Dan


[Edited by DANTRCAV on 02-15-2001 at 10:26 AM]

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Dan Taylor/ Tulsa, OK MBCA
'84 300D/'90 Jaguar XJ6/XJ40