pinging on an hill?

I only run premium in my car and here in NM that is a 91 octane rating. I buy my gas at a Shell down the street. I thought they had pretty good gas anyone hear different? My timing is good unless 12 and 35 are too much. Moper, I'm new to the holley carbs. I don't get any pinging unless I'm under a heavy load......all other times I get no pinging. Why the power valve first? I don't know the fuel circuits on the holley but, I would think that under heavy load it would be the secondaries that are too lean, help me out moper:)