Slant six timing issues

So update. Got it running driving and fixed some front suspension and steering along with new tires since my last post. Im trying to bring the timing in just abit more. The car hesitates on accelration and sounds like its going to stall , vaccum pressure drops then right as i let off the throttle my vaccum pressure goes back up and the engine sounds better. Any ideas? Is the fuel mixture too rich or maybe not enough advance?