Your solenoid is bad.
under the seat, connected to battery
Dont know. Just want to say that. 
The Yamaha Venture was manufactured between the years 1983 and 1993. This motorcycle was produced in two forms, the Mk1 and Mk2. The Yamaha Venture was brought back in 1999 and renamed the Royal Star Venture.
It is located over the front head to get to it both sides of the fairings has to be removed and the battery box. Its a pain
Begin with disconnecting the negative battery terminal. Remove the two bolts that hold the starter in place and also unfasten and remove the starter motor cable. The starter is easily pulled out.
No a Yamaha Blaster doesn't have a battery.
Your starter could be weak and need a rebuild.
Likely low battery- the click is the starter solenoid trying to pull in, but not enough current to turn the starter motor. If it will start with a jump, either battery or charging system needs attention.
from the Yamaha website
the little blue relay down by the battery and starter relay...
70 kg
I can't think of any that wouldn't fit. The 1986 to 1993 bikes are virtually identical except for colors.