Hi Greg - I do quite a bit of stabilizing for both call and pen making. You need to get as close as you can to "absolute vacuum", which is dependent on your altitude. For my altitude that's about 28.8.
You'll normally need a two stage vacuum pump to get to that point.
Unless you vacuum out as much air as possible, your blank won't be completely stabilized. You need to draw that deep vacuum then hold that until the bubbles stop coming out of the wood. Then after the bubbles have stopped you can remove the vacuum and allow the juice to get drawn in to the blank. Be sure and have enough juice in the chamber to keep the blanks well submerged, after I remove the vacuum I leave them sit overnight so they'll draw in as much juice as possible. Then I take them out, get off as much juice as possible, wrap them in tin foil and bake them @200F for an hour.
Happy Turning
Tom