I drill mine close to the edge that is off center. I use a 1/4 inch drill. Then when I find it bogs worse than before I stick a lead fishing weight in it. I've found that when the weights are to light the secondary weight trys to open to fast, by adding weight its the air flow across it slows down enough for the engine rpm to catch up. Same thing applies to Thermoquads, most people adjust the spring to light.