MG Car Repair: Trans controlled spark adv system, manifold vacuum, vacuum diagrams

Question
I have a 1979 MGB. The spark advance system has one hose from the distributor to a solenoid and another from the solenoid to a vacuum source. This end is loose. I've looked on the ZS carb and the manifold but can't find where it should connect. Thanks for you help.

Answer
Hi Scott,

On the 79 MGB you should have a Opus/Lucas distributor with the box mounted on the distributor with the vacuum retard unit on it. All vacuum retard units use straight manifold vacuum which will not be on the carburetor but should be on the intake manifold. You also have a anti-run on valve next to the bottom of your charcoal canister which uses straight manifold vacuum also.

There may be vacuum throttle switches and solenoids used by the factory to meet federal guidelines. You should have one vacuum port in the top of the intake manifold and then have a "T" to rout to other vacuum powered units (distributor etc). Older MGB's used a vacuum advance unit on the distributor and thus needed "Ported" vacuum which had to come from the carburetor near the throttle plate.

Most shop manuals are very poor in vacuum diagrams so about all you can do is be sure each vacuum operated unit gets the type of vacuum needed. The "T" connections were plastic and easily broken and then discarded. Most auto parts stores stock small vacuum hose "T" fitting.

Howard