maybe check the gear change mechanism, parts could be worn or rusted or even to much grease, the pawl could be worn. its easy to take apart and clean and put together just remember to re time the gears with the change unit, theres two dots you have to line up, if you take the cover of hold the kick start lever up a bit otherwise itl spring back
Replace the springs and check the square keeper plates are all flat and in place correctly on the gearchange mechanism. There's a thin headed bolt on the outside of the gearchange cover under the lever and on mine that regularly became loose. Tightening it up will improve gearchange positivity. CP gearchange has to be slow and very deliberate!
