Yeah it sounds like rebuild time !. The problem with hard starting could be Fuel percolation after you turn the motor off,fuel boils due to heat going to the top of the motor etc.. A heat sheild under the carb. will help as well as an insulated plate under the carb. The gaskets could all be suspect,with leaks etc.. The Power valve richens the Air/Fuel mixture when you "floor it". It's operated by "falling" vacuum. You will see numbers on it,such as 4.5,6.5,8.5 etc.. Use a vacuum gauge to see what your motor is doing. These numbers indicate the inches of Mercury (Hg)at which it opens. In fact what happens is High manifold vacuum at idle holds the P/Valve closed (inoperable),but when vacuum drops below the Power Valves Hg,it opens and richens the Fuel mix.
Now if it's opening at idle or off idle or leaking as they do sometimes (due to backfires through carb.)your motor will run rich,won't idle properly,won't respond properly to idle enrichment adjustments. I suggest buying a Holley carbs book,or borrowing one !!. Hope this helps you out.........Barry.M