Ported vacuum should start happening at speeds just a little above idle, and should be very close to full manifold vacuum when the engine is running at a steady cruise speed with light load. On a hard pull or quick acceleration the vacuum advance will go away, leaving nothing but initial and centrifugal timing. As soon as the load eases off, the vacuum advance will return. There should be little, if any vacuum advance while the engine is accelerating, so blaming hesitation or poor performance on the vac. advance unit is barking up the wrong tree. Late initial timing is much more likely to cause a bog on acceleration, or possibly a too-lean idle mixture setting could be to blame. Put a T fitting into the distributor vacuum line and attach a vacuum gauge to watch ported vacuum at work.
Jerry
