If the primaries are opened all the way and the secondaries are not, the progressive link must be bent out of wack, the wrong link has been installed or the arm attached to the secondary throttle pivot is spinning on the shaft (it's just peened on).
Get this fixed before you start to tune jets or power valves. A quick and dirty way to fix this fast is to have a buddy hold the accelerator wide open (with the engine off, lol!) and bend the link with two needle nose pliers until the secondaries are wide open.
If this is an older used carb that may have seen a lot of use, may I suggest replacing your base plate with a new one from Quickfuel? I have used their products and am very happy with them. The new base plate comes with three linkages, 1:1 (secondaries open in proportion to primaries), progessive (secondaries start to open @ about 1/2 throttle) and a super progressive (secondaries start to open at 3/4 throttle).
Older Holleys have seen a lot of abuse from over tightening, mongo return springs and mis-routed accelerator cables. All of these conditions cause exessive throttle shaft wear and vacuum leaks and lead to the I hate Holleys syndrome because I can't get it tuned/drops out of tune.
340s is right, it sounds like you're running lean, but get the secondaries taken care of first as it may be preventing your powervalve from opening by keeping manifold vaccum high.