Timing Advance Issues

[02coastie]

So I have a bit of a head scratcher:

74 w/002 Distributor (both vacuum advance & retard) with a Pertronix Ignitor.

I was setting the timing today and while at it doing some basic maintenance to the distributor. However, it appears my vacuum advance is not working. With the engine stopped and cap off, I can see the armature moving when vacuum is applied. However, applying vacuum while the engine is running produces no change in base timing.

I thought vacuum advance failures were almost always the result of a bad diaphragm. In my case, the armature moves, which would indicate the diaphragm is fine, correct? If the plate/ignitor is moving in response to the armature, how can the timing not be effected?

Thanks!
-Lloyd

 

[Honolulu]

Have you got the vacuum hose correctly connected, that is to the correct tube coming out of the carb?
Have you got the vacuum hose connected to the advance side of the vacuum unit on the diz?

 

[02coastie]

Have you got the vacuum hose correctly connected, that is to the correct tube coming out of the carb?
Have you got the vacuum hose connected to the advance side of the vacuum unit on the diz?

Yes, I actually used my mighty vac to apply vacuum to both the advance and retard port on the distributor. The armature moves in both directions, depending on which port I use. However, when running, vacuum applied to either port does nothing to change the timing,

 

[Stevehose]

when applying vacuum, does the distributor hold the vacuum if you pinch the hose? Is the linkage rod from the vacuum cannister inside the distributor connected to the base properly? I think there is a small circlip that holds it together. Pull the cap and rotor and check for movement of the plate when applying vacuum. Oops i see that your plate is moving....nevermind