service manual for F8B Yamaha 4 stroke

any idea where I can download a service manual for this motor?

my problem:
- the battery gets charged with 15.5 Volts....too high! how to lower the voltage? and
- the choke seems to stay engaged for minutes instead for seconds, so the motor does not run well for minutes, sometimes for one hour

(problem with part 24? electrical valve ?:

http://www.boats.net/parts/search/Ya...TOR/parts.html
)

drawing seems similar to my F8B motor.

thanks a lot!!