The valves can either be too loose or too tight. If they're too loose, you will hear them. If they're too tight, it will start getting harder to start. Valve clearance should be checked periodically, even if you don't hear them making noise. Also, an exhaust leak up close to the head can cause a popping when you let off the exhaust. check for a crack in the pipe where it bends back around to go into the head, I've seen them crack there. In addition, check to make sure the bolts that hold the exhaust to the head are tight, but be careful not to twist them off. They twist off pretty easy.
An occasional pop is normal, especially if you were wide open and let off the throttle quickly.
An occasional pop is normal, especially if you were wide open and let off the throttle quickly.
