Converting 1999 Force/Mercury 40hp to 50hp

[GoFastr]

Read several older posts about it. "Seems" like the only difference between the factory stock Force 40 and the 50 is the carburetor part numbers, and all other common main parts are the same. I'm thinking about ordering a 50hp carb and slapping it on to see what happens. One poster from 2008 said he got plus 3-4 mph after changing just the carb.

Was wondering what who has done this and what their results were as well as what it's used for. Mine is on a 1999 Sun Tracker 21' Party Barge pontoon boat.

 

[jerryjerry05]

Re: Converting 1999 Force/Mercury 40hp to 50hp

Powerhead's the same.
Carb is the same(obsolete or NLA),just change the jets.
.062/40hp to .096/50
Under $6 at boat . net

Now with all the extra horses you might invest in a neck brace!!!
Those take offs are gonna be tough

 

[roscoe]

Re: Converting 1999 Force/Mercury 40hp to 50hp

I only know of 2 motors out there that actually have all the same parts and you can try to convert like this.



NMMA hp standard is +/- 10%.

So if the 40 is really 44 hp, and the 50 is really 45 hp, the conversion should be really simple and easy as you only need to get 1 or 2 extra hp out of it.

But if the 40 is only putting out 36hp, and the 50 is putting out 55 hp, the conversion is going to be hard to do. You just aren't going to pull another 10-15-19 hp out of an extra drop of gas.

Your best bet is to increase the jet size one size, and get a prop that will put your wot rpm up around 5600 rpm, and be happy with it.

You will never know how much it helped the hp output, unless you dyne the motor before and after.

 

[GoFastr]

Re: Converting 1999 Force/Mercury 40hp to 50hp

yeah understood, but if there's a miniscule investment of timme and effort and i still get a tad bit more umph out of it, then it would be worth it.

Right now the local prop shop gave me a 12.5 x 8p prop based on size, year, hp and normal carrying weight and said it should slightly over rev with a light load, and then come down within range as more bodies are added. It came to me with a 10 7/8 x 11p that had a chip on the tip of one blade.

Well i went out yesterday and tried it myself and two other adult and 3/4 tank. It fluctuated between 13-14mph on the hand held GPS, but the tach was only showing 4600 rpm's wide open and adjustiung the trim. Called the prop guys up this morning and they said that sounded odd, and that I might want to verify the tach accuracy and/or ensure the throttle is opening up all the way etc. etc. before I go chasing the prop angle. Not sure how i would verify the tach on an outboard. Anysuggestions?

 

[emoney]

Re: Converting 1999 Force/Mercury 40hp to 50hp

The only way really to know is to check it with another tachometer. That's a heavy boat so did you tell him what it was going on?

I rented a pontoon once and I don't remember even getting that speed so you might be doing better than you think as 4600 is probably the bottom of the spec range? I'm just supposing though so wait for one of these smart guys to weigh in.

 

[jerryjerry05]

Re: Converting 1999 Force/Mercury 40hp to 50hp

To verify the tach.
Some timing lights have a tach built in.
Or another tach?
Or a Tiny Tach.Great thing to have.
Not sure if they sell them here but Amazon does.
Just make sure it's for your app.

LIke i said the powerhead are the same Part#s and the only difference is a main jet.

But like the other have said make sure it's reaching WOT.
Too much weight and stuff in a boat will kill the power.

You know the amount oF HP your gonna get aint worth messing with.
Get a bigger motor!
Lots of good stuff out there.
In fact i have a great 85,just a little older 1972

 

[GoFastr]

Re: Converting 1999 Force/Mercury 40hp to 50hp

Ha! This is my second boat. The other is a twin big block offshore go fast boat. The wife sez we're not investing in any motor upgrades on this one, especially since I talked her into it because I pretty much stole it and promised other than some elbow grease, it would be an inexpensive yet enjoyable "party barge". So the minor effort of a "possible" couple unnoticable hp will help me sleep at night knowing I got her wrung out.

I've got a digital timing light I haven't used in years and not sure if it has a tach option or not. I'll have to google some other McGyver type tach options.

 

[Faztbullet]

Re: Converting 1999 Force/Mercury 40hp to 50hp

LIke i said the powerhead are the same Part#s and the only difference is a main jet.

The carb is the only difference as the venturi is bigger on the 50 carb than a 40....

 

[Frank Acampora]

Re: Converting 1999 Force/Mercury 40hp to 50hp

20% increase in horsepower due to a carb change? Out of 49-51 cubic inches? That's a lot. I don't know for sure, but I would not be surprised if the 40 block (which does have the same bore and stroke) was ported more conservatively.

Also, if the 40 has a small bore WB type carb (1 5/16 venturi) and the 50 has a big bore TC type carb (1 5/8 venturi) the manifold cover will need to be replaced, since the mounting is so much larger for the TC.

 

[djben]

Re: Converting 1999 Force/Mercury 40hp to 50hp

Powerhead's the same.
Carb is the same(obsolete or NLA),just change the jets.
.062/40hp to .096/50
Under $6 at boat . net

Now with all the extra horses you might invest in a neck brace!!!
Those take offs are gonna be tough

I tried the carb-only change and it didn't work, motor just didn't run right. I suspected the carb body was actually different (TC131A on the 40hp, TC134A on the 50hp).

I found someone selling the TC134A on ebay for $90. Got it in, rebuilt it with a combination of two rebuild kits on Amazon (same ones I used on my 40hp), and prepared to install it on my motor.

The carb body is actually different - the housing has a larger diameter intake. All other aspects of the carb body appear to be the same, with the exception of course being the larger diameter jet. See attached pics.

Results? Using GPS, I was getting a top speed of 30mph on my 1996 Tracker Pro Team 17, and with the 50hp carb I'm at 34mph with what appears to be +200RPM on the tachometer. I'm going to update my prop from 15 pitch / 10" diameter to 17 pitch / 10" or 11" diameter and see how things go.

It's my first ever boat and I figured it was worth a shot. So far so good today, burned through a bunch of gas doing some high speed runs on the lake

Thanks all on this thread!