I agree w/ slinger. There may be a bent valve stem, weak or broken spring, worn cam, or bent/miss cast rocker arm. If the valve is catching air in the the cycle, it will most certainly tick when it re connects w/ the lobe. I can think of 2 ways to verify w/out major surgery. One would be to use some 1200 grit emory cloth to remove the shine on both lobes. Just remove the shine. then run for a few km, and see if it is polished back up, or using a timing light w/ variable timing to "freeze" the action. Does the sound amplify w/ rpm's? if so I bet you found it! The first method may seem a little drastic but I have cleaned many a rusted old cam for re use using emory cloth w/ no ill effects. On every high performance engine I have ever assembled there is no free time for the valves except for tdc. If there is then a stiffer set of springs gets installed. Now to qualify all this the Kymco engine is a compromise by design. It's the best it can be for the $'s charged. The springs may be marginal to begin with to save wear on the cam/bearings. I always try to get my info from the horses mouth vs the other end, so perhaps a phone call to kymco usa tech support could help. This just may be normal for the engine, although I would not believe so.
