With the hand-change box there is little or no need to use the clutch when changing up, but changing down, especially at higher revs, does benefit from using the clutch, especially with the wide-ratio box. The ‘old school’ riders would use their LEFT hand, across the tank, to change gear, but this is not so easy with wider Rep tank, compared to the earlier vintage slim Flyer tank. Another old way to change up without having to ease back the throttle was to briefly use the magneto kill switch instead. This however tends to cause loud bangs in the exhaust ! Why are you using the advance and retard lever ?