Also you will see some vacuam to the advance even at WOT. but as mentioned it needs to be connected to ported vac. and can be limited in total advance as well.
You shouldn't see any additional timing from the vacuum advance at WOT. If you have much more than 1-2"Hg of manifold vacuum at WOT your carb is way undersize and is seriously restricting the engine (for max performance you would shoot for no more than 1/2" Hg). Stock setting on a vaccum advance is 5-7" Hg, don't think you could adjust one down to the 1-2" range.
