On average, how fast should I be able to go at WOT?

Joined
Jul 22, 2020
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6
So I have a 17 ft Maxum with a 85 HP force outboard. I also have a 17 prop on the engine with electric Trim. At WOT, I’m topping out at 4000rpm and around 27 mph. To me, this seems a bit slow and low on the RPM and max speed. I understand there’s a lot of variables here but what are your options on what my WOT speed should be with this set up? Thanks
 

jerryjerry05

Supreme Mariner
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May 7, 2008
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17,923
4000 is about 1500 too low.
Check the compression and spark on each cyl.

That boat should do close to 40 when running right.
 
Joined
Jul 22, 2020
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6
I did a compression test. 120 on all three cylinders. I also changed the spark plugs out and drained the fuel thinking maybe I got a bad mixture or something. The dam thing runs ok it just fills like it doesn’t have the balls to get rolling line it should.
 

The Force power

Commander
Joined
Feb 3, 2019
Messages
2,241
Are the Carbs. set-up right? butterflies all the way open?
As Jerry already mentioned; do you have spark on each Cylinder?
 

jerryjerry05

Supreme Mariner
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May 7, 2008
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17,923
The amount of foam in these little boats is minimal.
The amount of water they would hold isn't enough to slow
the boat down like this.

Check the linkage and make sure it is operating correctly.
Run with the cover off and look at the linkage to see if the carbs/linkage
is opening the butterfly's correctly?
 
Joined
Jul 22, 2020
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I tore out the flooring a month ago when I boat it and replaced it with 3/4 inch treated plywood. There was some foam but like Jerry said, very minimal. I put down new carpet while I was at it. The old flooring was a bit rough and saturated but it is a 30 year old boat and almost looked original if you ask me. I’m starting to sense there may be a timeing issue and possibly a fuel mixture adjustment needed.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
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47,304
if the old floor was rotten, the stringers and transom rotted about 10 years prior to the floor.

so what you did was a deck-over?
 

The Force power

Commander
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Feb 3, 2019
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2,241
I have a 18' Bayliner with a 85/90 hp and saturated foam /extra plywood. (lol)
Mine will run 36 MPH & "trimmed up" 37 MPH at 5500 RPM's
It not the boat causing this; it the engine not being tuned right.
 

WinnerCougar74

Petty Officer 1st Class
Joined
May 12, 2020
Messages
204
I have a 1974 Winner Cougar with a 135hp Chrysler. iBoat specs say 2500lb boat. It came with a 13x19 prop. WOT with that prop was 4500rpms @ 38mph. Recently bought a 13x16 prop. Now 5500rpm @ 32mph with significantly better holeshot and overall just feels better and I think is easier on the old 1974 Chrysler motor. With the 13x16 it does seem to want to rev past 5500rpms (which scares the crap out of me) and loose some gas mileage. 13x17 is probably perfect.
 

WinnerCougar74

Petty Officer 1st Class
Joined
May 12, 2020
Messages
204
Not being able to get 5500 rpms from the 13x19 prop makes me think the engine is not putting out the power it should. It has always seemed smoother and better running at about 4000 rpms. With the old motors it seems like there is no way to really know. I guess if everything is setup right, timing, carb sync etc then just run it and be glad it still runs ok. A replacement would be many thousands of dollars. I'm going to install a kicker motor. Better for skinny water, trolling and backup if the old chrysler dies out on the water.
 

125

Seaman
Joined
Jun 25, 2020
Messages
73
I have a 170 bayliner 125 force runs like a dream good compression no misfires but is really starting to lack power both hole shot and top rpm only make 4000 rpmowned engine from new can barely make 35 mph and take# forever to get there now
 
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