1985 or 1986 Force 125 is slow on 180 Forester

Spivy30

Petty Officer 1st Class
Joined
Jul 19, 2008
Messages
299
I am trying to figure out what is the problem with my boat it is a 1986 Forester 180 Phantom with a 1985 or 1986 Force 125 with just myself in the boat and a 1/4 tank of fuel I can only get 32 mph out of the boat on the gps and a wot of 4100rpms
The prop has no size stamped on it but on the hub it says "michigan 072107" so I checked to see if that was a michigan wheel number and it was a 17pitch prop for a force outboard. I just dont understand how the boat could be so slow. According to a forester brochure it says the boat weighs 1090 pounds without motor so I figure about 1500 pounds with motor and fuel to be on the safe side. My dad had a 1985 bayliner 19 Capri with the same motor and it did close to 50 mph.
My guess is the boat is totally proped wrong but i've read so many different things I dont know what to believe. I would also like to add that the boat has 150lbs of compression in all 4 cylinders, new plugs, and runs on all 4 cylinders

If its not a prop problem what could it be motor starts, idles, and runs great

somebody please help
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
Re: 1985 or 1986 Force 125 is slow on 180 Forester

If the tach is reading right then you need to reprop.Is the prop stainless or aluminum?
Acording to your tach 4100rpm at WOT then the prop could go down in size to a 15p or even a 13p. Jerry
 

Spivy30

Petty Officer 1st Class
Joined
Jul 19, 2008
Messages
299
Re: 1985 or 1986 Force 125 is slow on 180 Forester

I think the tach is reading right because it doesnt sound like i'm getting very high rpms, the prop is aluminum, if I go to a lower pitch isnt that a really low pitch for a boat this size
 

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,657
Re: 1985 or 1986 Force 125 is slow on 180 Forester

I would suspect a fuel delivery problem. Or..., you have waterlogged flotation foam in the hull.

Time to check the carb butterflies, are they opening all the way?
Is the throttle/timing linkage advancing properly?

Your boat motor fuel battery weight, is likely 1600#. Plus any water if the hull is waterlogged.
 

GrindKore

Petty Officer 1st Class
Joined
Jun 20, 2008
Messages
211
Re: 1985 or 1986 Force 125 is slow on 180 Forester

Also, check your compression. I had similar issue recently and tried different props, however the real problem was busted piston rings. After I have rebuilt the power-head with new pistons my WOT RPMs are back to normal range and the motor runs very smooth.
 

Spivy30

Petty Officer 1st Class
Joined
Jul 19, 2008
Messages
299
Re: 1985 or 1986 Force 125 is slow on 180 Forester

I dont think the boat is water logged it was always stored inside, as far as fuel delivery thats always a possiblity but it flies out of the hole and gets up to 35 very quickly just cant get more than 4100 rpms. Just did another compression test and got 150lbs across the board. I made sure the butterflies were open all the way.

I dont know what to do

should i go to a lower pitch?
 

Spivy30

Petty Officer 1st Class
Joined
Jul 19, 2008
Messages
299
Re: 1985 or 1986 Force 125 is slow on 180 Forester

Last night I had the boat hooked up to the muffs and it ran up to 5500 rpms just fine so I think I can rule out fuel delivery
 
Top