more hp less speed

[ooneill]

I have a 1994 sweetwater challenger 20 ft. It had a 40hp force by mercury motor. It ran great at the river but when the day was ove rit took to long to get back. I found a 1994 force by mercury 120hp. I swapped out the motors using my extisting controls. I ran the motor at home ( out of the water) and the engine sounded great idle was smooth, I dropped the prop in my test pool and every thing was good. sorry I do not have any numbers. When I got her out on the lake at full throttle the boat felt slower than with the 40hp. It sounded like it wanted to open up and fly but just wouldn't. Any ideas on what the problem is.

 

[45Auto]

Re: more hp less speed

What size prop is on the 120? What kind of boat did it come off of? Did you buy a new prop sized for the pontoon or are you using the prop that came on the motor? If the motor came off a typical 17'-18' V-hull boat, it may be way over-propped for the pontoon if you didn't change props.

 

[5150abf]

Re: more hp less speed

Agree, it sounds overpropped, it's like if you tried to drive your car up a steep hill from a dead stop in 5th gear, the engine just doesn't have enough power to over come the high gear and the load.

Is your transom rated for that big of a motor, if not this may not be a problem for long since you will be trying to fish your motor out of the lake.