Several weeks ago this bike became hard to start toward the end of a day of riding. I checked the valve gap and found the right intake was tight at 0. I reset it and the bike started and ran great except there was a slight ticking noise. After 3 or 4 riding trips the ticking noise became more noticeable, so I recheck the gap and found the right intake was slightly tighter than specs. I reset it again only to find the ticking noise became much louder and was noticeable when I rode around the track. I checked the gap again (always at TDC) and this time it was perfect. Anyone have any idea what might be wrong? Background info: I replaced the titanium valves with stainless steel about 3 years ago. I have taken the clutch apart, the right-side cover, and the top end looking for possible problems but to no avail. Next, I am going to remove the left cover to see if there is something loose or amiss around the flywheel. I have checked the crank and the bearings appear to be good...turn easy, no noise.