Need some advice

[longtalltexan]

I have a 1985 25 HP merc. on a 16 ft. flatbottom boat. The boat will only top out at about 5 mph. I turn the throttle almost to the max and it goes 5 mph. when I finally max it out the motor will rev up but will not accelerate any. Any clue on what the problem may be or possible fix?

Thanks for any help!

 

[smartcaddie]

Re: Need some advice

couple of things for you to check.. first the height of the transom and of the engine. make sudre that both are correct for each other, ie: 20"shaft with a 20"transom. and now check that the prop is ok and have no dings on it. that could slow you down and finally.. how much weight are you adding to the boat? that can be a big one..

 

[Mac uk]

Re: Need some advice

And theres Hull design. I read in a boat book that the design of the hull determines its speed and no matter what engine you put on the back it wont go no faster, so I read.

 

[MIKEY*2007]

Re: Need some advice

there are hub bushes on props if it it slipping u go nowhere try turning prop in gear if prop turns and motor does not turn over u have broke it, take plug leads off first so motor can,t start

 

[Riverman128]

Re: Need some advice

I have a 1985 Merc. XD on a 1542 aluminum Jon boat. With me and lightly loaded, it will run 29.2 MPH (GPS) with a 15" SS prop at 5560 RPM. Check to make sure you have fire on both cylinders. I could not get on plane this summer and found no fire on #2 cylinder. Bad switch box. It would be a good idea to check compression.

 

[mthieme]

Re: Need some advice

We need much more information.
What kinda boat, how is it outfitted, prop type (or numbers off the hub), has it always done this or did it just start, etc.