MG Car Repair: distributors, advance mechanics, vacuum advance

Question
I have been working on a stumble issue that you have been helping with. In the course of this I have realized I have a distributor issue and can't seem to get it correct. Car had electronic IGN replaced with a points dist many years ago. In the course of this modification someone determined that the vacuum advance no longer needed to be used. So the line was discontinued and no longer runs to the distributor. Before I decided to reconnect etc. I thought I had better inspect the distributor unit before proceeding.  The dist. was MFG'd in 1971.  There are no mechanical parts inside the dist for the vacuum advance to even function. The advance mechanics deadend at the arm as it enters the dist. There is nothing to attach to so it can not advance anything. The cam is a 18 degree mechanical advance which seems high to my uneducated mind. ( Another dist that I have has a 11 degree cam for the same year car# Inspecting further I feel no vacuum from either the Carb port or the manifold port. Is this just slight pressure ? How much can or will these vacuum advance units really move ? Both units I have looked at #one in the car and one not ) seem to require a great amount of force to activate.  I had read somewhere that the unit could be checked by blowing into it. That sure would not be the case with these !!! Just old and wore out ? Car is a 79 Midget with 1500 series engine with 25 D points dist. Should have a 45DE electronic dist. Manual shows manifold vacuum advance to distributor , although it also seems that ported vacuum would work as well. Thoughts and advice, Please  

Answer
Hi Mark,
If a distributor has a vacuum advance unit on it, then it will have a moveable points plate. Get a service manual and compare the parts in your distributor with the manual or look at some of the parts break down pictures on some of the British parts companies on the net.

A vacuum advance unit is powered by ported vacuum on a carburetor, which only has vacuum when the throttle is slightly open and a vacuum retard unit is powered by direct manifold vacuum. Sometimes you can't feel the vacuum very well so you need to buy a vacuum gauge.

The reason most people switched from the electronic ignition to points is because the electronic ignition was very unreliable.

Total advance is the most important item and everything below that is secondary and only for derivability.
Howard