One week and one day with my ´13 Yamaha 650 Custom, running a little bit smoother with 320 miles now, but 4 valves would do the trick. Will keep for a year and will then move up to the 800 C50T Kawasaki 900 Vulcan or the Yamaha 1300 Star Deluxe... What ever it is, has to be liquid cooled and four valves.