Hi DJ1984 and welcome to our lovely home of outdoor stuff,especially mowers.Well it is for me anyway.You will find on here a couple of Scott Bonnar fans on here.I'm sorry not me although I'm becoming quite knowledgeable on the Scott Bonnar rotary's.I do believe they ran for quite some time so as far as year I have no idea.If I'm correct (and I may not be)there should be some numbers on the cowl.Most likely on the carby side.If so pop them up,that should help ID the year and model number.If not I don't know and (I'll shut up)and I'll leave it to the people who do know.Like Deejay his the man to know.
Thanks and again welcome aboard.You'll will find you will learn a lot here.It's a great forum.Enjoy.