I have 1972 Honda 350 cv. When trying to start fuse burns out. Replaced ignition switch. Same problem

 

Sounds like a short in the solenoid control wire or the heavy starter wire. Can you turn it on without blowing the fuse? If you can, try shorting the heavy contacts on the solenoid momentarily. If that kicks the starter on without blowing the fuse, the heavy wire is probably good. That means your switched control wire from the started has a short to ground somewhere between the starter button and the solenoid.