You have to be patient. Stonefish is right about waiting for the commotion to settle after casting. Many times, they will hit it as soon as it hits the water, and other times, they will need to be enticed. In either case, a pause before retrieving seems to be effective. Also, keep in mind that bass will often take a pre-emptive strike at a popper (especially a larger one) to "stun" it before returning to engulf it. Trout will do the same thing with large bugs like adult damsels and hexagenia, which is one of the reasons many people have difficulty hooking fish during the Merrill Lake hex hatch. Wait until you see your popper disappear before striking. They generally aren't too quick to spit them out once they decide to eat them. When you do get over-excited and strike before a fish fully takes your popper, cast right back to the same spot. Bass are aggressive critters, and they will often take follow-up presentations with reckless abandon.
To Skysoldier's point, I have also done better on bass using large streamers and smallish pheasant tail nymphs than poppers. Muddlers are a favorite go-to, as they are easier to cast than big, bulky leech patterns and allow you to fish with, say, a 6-wt., as opposed to a 7 or 8, which takes some of the fun out of fighting all but the biggest fish. All that said, it is great fun getting them off the top, so you should definitely keep giving it a fair effort. In my experience, bass are also much more apt to eat off the top at first light and dusk than at any other time of day....
