Valve bounce happens usually at high engine rpm and involves the combination of valve mass and valve spring constant. The valve literally hits the seat upon closing and lifts off the seat to then close under spring force. Ducati has a "desmodromic" system where the cam opens AND closes the valves to eliminate the possibility of bounce. Springs are cheaper and lighter and can be made with different rates to eliminate bounce at high rpms. Honda and Kymco have figured all this out years ago through racing and testing so I don't think we have to worry about valve bounce. Plus our machines have rev limiters to keep the revs below 9-10000 rpms.
Karl
