Home › Forum › Ask A Member › 18HP saga continues. Can’t get past 14mph and 3,900 RPM. › Re: 18HP saga continues. Can’t get past 14mph and 3,900 RPM.
If the same problem is on all three powerheads, are you using the same mag on all three? Is the mag plate worn and wobbly causing erratic ignition timing? New coils, points condensers. What about new plugs and plug wires? A new set of NGK B8S might help along with new copper core wires. If the wires seem good, corrosion can build up under the spark plug boot causing all kinds of electrical problems. Maybe pull the wire and terminal out of the boot and then trim a half inch or so off the end of the wire before reinstalling the terminal. It seems strange the issue follows all three motors.
The crank in your ’61 motor has needle and roller bearings throughout and originally used 24:1 mix. ’64 was the first year OMC called for 50:1 in their motors, using proper outboard oil.
How heavy is the boat and would the prop have too much pitch for the load causing the motor to lug? An eighteen should push a light boat around 25 MPH and a 15 about the same.
https://www.youtube.com/watch?v=pxLdVbqhC_g
https://www.youtube.com/watch?v=p96DIKwaR9E