The muffs work great on my 90HP Force. I figure if water's coming out the pee hole it's getting plenty. Now my 62 yr old 'Rude won't take muffs due to the intake design so I use a metal 1/4 drum for it. I leave the motor on the transom, slip the drum up on the LU, slip a milk crate under it and fill it w/ water.
Mike
What was probably meant by not enough water flow was for wide open throttle. Muffs can be used on I/O's, mine is a 140 hp and my neighbors is a 250hp and muffs work fine but NOT enough water flow for continuous high speed engine operation. Idle speed is fine or a slightly about idle speed is fine. I have blipped my throttle up to 3000 rpm on muffs but do not leave it there. Unless your running that OB at high rpm you should not have any problem at all.
I work at Washburn Marina, Washburn Wi. The gateway to the biggest waterpark in the great lakes! Lake Superior. The Apostle islands are just 30 min away by boat. If ya throttle it a bit, usually I take in the scenery, a bit on the way....washburnmarina.com
I'm from Minouqua and used to go to your area quite a bit in the summer and loved it. Now I've got to live in Florida as my wife makes me. I still miss it up there. I was pretty good friends with Ross Marine in Washburn.