I will allow myself one guess (assuming motor is in good running order
properly mounted on a sound boat suited to power of motor) I would look at
propeller and clutch...starting with the prop nut, metal washer and rubber
bushing in base of propeller. These items are part of a system that clamps
the clutch together...photos of lower unit should explain matters,
Louis, you may be on to something. The boat is rated for only 3 hp. The engine seems quite deep in the water when stopped. Only the top two exhaust relief holes are above water. The more power I apply, the more the boat plows. The motor doesn't act like there is any slippage, it acts more like the prop pitch is too much.
My neighbor has a similar boat with a current model 4-stroke Yamaha 4 or 6 (I'm not sure which). I want to race him, but I don't want the old Wizard to be embarrassed. It seems like his boat goes much faster observing it from afar. His boat is probably rated for the engine.
Cavatation plate even with bottom of boat?
Mercury Service Manual has a section covering set up of motor and possible
problems with boat bottom bumped in or bumped out (called hook and rocker)
Depth of prop and angle do matter as does tilt of boat...a little ballast
far up front may be needed.
The washer used to compress rubber bushing in rear of propeller is not a standard size (Kiekhaefer liked to do things their way). The hole in washer
is a loose fit on prop shaft but the outside diameter is small enough to
fit into propeller cavity to compress bushing. That way the clutch is held
in compression so prop will not slip under power. If the prop strikes something the clutch gives and a level of protection to drive train. A little more
elaborate than a simple sheer pin. No on the water sheer pin replacement though.
Racing...cheat a little get an after market prop designed for a little more
get up and go. Michigan Wheel made a wider variety of props for the early
outboards than Kiekhaefer some of which were designed just for what you
have in mind...a little better performance on a light boat with an essentially
Louis, thank you for helping me sort this out! With your advice I doubled my top speed. I can go 14 mph! I removed the in tank filter and installed an inline filter. I tilted the motor down to get more up thrust on the stern. I made an extension for the tiller so I can move forward to plane off. For safety I tied a piece of string to the throttle handle so I can reduce speed if I'm in the middle of the boat. Once I get up on plane I can move aft and still go 10 or 11. The cavitation plate is about 1.5" below the bottom surface of the boat so that's probably a big part of my trouble. But I now I know the Wizard is capable of much more than I was getting. I still have a problem with the engine stalling at full throttle, but I will start another thread for that.
I'm really happy with my Wizard now, it's fun and exciting to ride now. Thanks for the guidance. When you double your top speed it's a good day!
On my 14' Jon Boat I am running about 20 MPH with mine. I weigh 200 pounds.