1996 40hp Mariner magnum

Good Morning. I have the 40hp mariner on my 1996 24' Harris pontoon. I picked this kit up this spring and it worked fantastically all summer. Just before I was to remove the boat from the water this fall, I noticed the motor was 'slipping' for a better choice of words. The motor would run fine at lower RPM's but if I pushed the throttle open, then it sounded like the motor would suddenly over rev like the prop was disconnected. Then as I brought the throttle back down, everything would return to normal and the boat would still move. It felt like a really bad slipping clutch in a car. I'm not to informed on boat motors as this is my first year on the water. I am very mechanically inclined though. Carpenter/welder/electronics/all round handyman. I just don't mess with things I am not certain about or have the correct info on first.
I can easily pull the lower end off if that's what is entailed to send to a marina if necessary, but if it is a do-it-yer-selfer, I can do it. (I never hire people if it is at all possible to do it in my garage)
Any input would be greatly appreciated. I'm headed to the Toronto Boat Show this afternoon and someone may have a suggestion for me, but it would be a one time conversation. No follow up if I need it.

Cheers folks.

Re: 1996 40hp Mariner magnum

Sounds like a prop with maybe some damage causing severe cavitation, prop hub is failing or bottom growth or hull damage interfering with water flow to prop..

Re: 1996 40hp Mariner magnum

Thank you for your input Faztbullet. I thought about the prop point you mentioned, but not being a pro on the physics or experienced on it, I didn't think it made such a difference. The prop isn't perfect, so it may be just that. Since I just wanted to enjoy the boat last summer, I put off replacing the prop for this season. It'll be easier while the boat is on dry ground at the cottage. I had to have it delivered on a rented trailer so I couldn't do little things like replacing the pitot as well. The prop was also on the list.

Re: 1996 40hp Mariner magnum

Faztbullet nailed it..very simple...Spun Prop Hub...buy a new one unless you have a friend in the business to repair yours