I guess the way you described the problem was very vague, and out there, it dosent tell us what you tried to do with it, what you checked for, how long it had been sitting, or even why you think the magneto may be bad. Does the machine have spark? Getting clean gas? Air filter free of obstructions? Got good compression? There are about a thousand things it could be as of right now. WE NEED MORE INFO.
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