Prop Cavitation Problem / Exhaust Seal

I have a stratos with a 2000 Evinrude 200HP on it.. I changed the lower unit out and put the prop on and there is a large gap ( 5/16 to 1/2) between the prop and the lower unit housing.. It seems like my boat is cavitating on hole shot and I have to feather my throttle to get it to catch back up.. I believe that the exhaust is escaping though that gap between the prop and housing.. Read somewhere that there is suppose to be a exhaust seal in this gap??? It looks like the lower unit is threaded on the inside for something, could there be a seal that is suppose to be threaded in there??? Boat runs great after I'm on plane.. I thought at first the rubber went out in the prop so I had it redone by power tech in Shreveport so that's not the problem.. Any help would be appreciated.. I don't have the old lower unit so I don't have anything to compare it to that is real close by..

Re: Prop Cavitation Problem / Exhaust Seal

I can't speak specifically to the 200 but I can't recall any prop seal on any gear case.
My first guess is you have a prop intended for a smaller gear case What size is the prop?
Perhaps you have the wrong thrust washer?
Perhaps the wrong gear case?
This may be more a motor question than a prop question.
Post your problem in the Evinrude/Johnson motor repair forum.

Re: Prop Cavitation Problem / Exhaust Seal

What you're referring to is called a weed guard. I use one with my Renegade prop for just the problem you're describing. It fits into the lower unit before the prop is installed. There are a couple of different sizes of them to fit different gearcases.