Try turning the shaft that the clutch sits on, while at the same time turning the star. It should click into gear. You could also try turning the shaft the sprocket sits on, while turning the star piece, and that may work. One way or another, it should shift with these methods if everything inside is indeed correct. Good luck!
THE 80's RAGE! Currently owns:
81, 85 Yamaha Tri Moto 125
83 Yamaha Tri Moto 200 x2
82,83 Yamaha Tri Moto 175 project
85 Yamaha Tri Z 250
84 Kawasaki Tecate 250
84 Honda ATC 70
85 Honda ATC 350X
84 Honda ATC 250R
(2) 84 Honda ATC 200x
82, 83 Honda ATC 185s
81 ATC 200
Lots of other parts and bikes