I'm not too sure if you bike seat is the same as mine (78 550).
But, this is what I did.
I took the hinge pins out - took a flash light, flat screwdriver, and a bunch of time.
Once the pins were out, I lifted the hinge side of the seat about 2 inches.
Then took a wrench and slowly loosened the bolts holding the locking pin that is attached to the seat.
Presto - seat is off.
Mind you this is off a 550.
If the seat is completely different on a 750 - sorry, and disregard this post.