Vacuum Problem?

Well you need to "whut" and to SET the timing. You SET the timing FIRST. If for example "you used to" run it some what advanced, and now your friend has set it "more stock" (IE retarded) that might well be part of the problem. "The thing" about timing is if your car has a factory distributor then it is a "smog" advance curve, not ever ever designed for performance. Even so, I would bump the timing up to at least 8 BTC

It "could want" more initial advance, but then might OVER advance unless the distributor has been "re curved." ALL FACTORY DISTRIBUTORS suffer from this problem in the "smog" years 68 and later, and "gets worse" in the mid -70's and later.

And you don't "play around" with idle mixture. Mixture is adjusted by a PROCEDURE. After setting the timing, you get the car fully warmed. A good mechanic sometimes uses "by ear" but you should use either or both a tach and vacuum gauge. Adjust first one, then the other MIXTURE adjustment for maximum vacuum and idle RPM. RE adjust the idle SPEED screw to keep the idle where you want. The mixture screws should be "touched" last "towards" lean "just at" the point that vacuum or rpm just starts to drop. "Back and forth" on the screws is often needed