Oil pressure vs lifter pump up
As I stated before if your valves springs are weak and your valves start to float your lifters are taking up the clearance to the point were the lifter tops out on the snap ring. The speed trick that perfacar is talking about works because since the lifters are already topped out they can't take up anymore clearance that might be added by weak valve springs. Since the lifters can't take up anymore clearance the lifters won't hold help hold the valves open. Bottom line is the springs are supposed to return or keep the valve train in check, you need better springs.
Chuck