What has been done to your distributor , is it the stock unit for your engine or ? If it's the stock unit and you have not done anything to limit mechanical advance you will get too much advance , stock dist. have 30 and/or more degrees built in.

As far as the different readings from one side to the other , it's supposed to be that way . The drivers side port is manifold vacuum and the pass side port is timed vac that will not see full vac till the throttle blades are open a certian amount .

you might want to put a REAL vac cap on it instead of that hose wit ha screw jambed in it .