You should be able to score a clutch cover for under 100 dollars on ebay easily, if you keep an eye out. It could have low compression also, if the kicker works fine, which is why he would have to pull start it. Yes, the R on the end is a typo, but the tri z is yamahas fastest and only race trike.
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