Avs2 650 tuning on a 340

If hooking up VA made zero difference, then the VA is not working. Ruptured diaphragm or insufficient vacuum to pull in the VA.

Here is the good news. You can have your cake & eat it too!

Please read the link below FIRST, & then come back to here.

You need an adjustable VA unit, connected to a manifold vacuum source. Adjust the Allen Key fully CW. Trying to do this with a factory VA unit & 10" of vac will not work.
You use the VA unit to provide the extra timing that you found [ earlier ] that the engine likes. You can use any combo of VA + initial to give you the desired idle timing, while keeping the starter happy. Example, if the idle sweet spot was 34*, then you could use 14* initial + 20* VA. You will probably have to fabricate a movement limiter for the VA actuator.
Contrary to an earlier post in this thread, adding VA in the above manner can cure an off idle flat spot. I have done it many times. What happens is the engine is making more HP with the extra timing & the extra HP allows the engine to carry the load, so no stumble.

Yes, there is a bit of messing around to get this right but that is what hot rodding is about....

www.hotrodders.com/forum/vacuum-advance-hooked-up-directly-manifold-bad-47495.html
Scroll down to post #6.