Popping on decel, usually result of fuel-lean idle mixture, as Spec says above; cured by removing the tamper-resistant plug, bottoming (gently) the fuel screw (underside of carb, engine side), and gacking it out 1.75 turns or so (for stock engine starting point).
Google, "Care and Feeding of the CVK40" for a readable primer on your carburetor.
A separate component, the "Air Cut Valve," or "Coasting Enricher," or "Backfire Preventer" handles mixture management on deceleration in a larger way, but . . . mild popping can often be cured, or greatly reduced, by backing out the fuel screw.
That said, mild backfiring upon deceleration remains operationally benign, IMHO. Don't hurt nothin'!