Converting a tohatsu 2.5 to 3hp?

[b.gagnon]

Can changing the carb on a mid 2000's 4-stroke tohatsu 2.5 turn it into 3hp?
I am buying this as a project for my son. I want him to learn how they work (I own a 2015 3hp merc). The owner says it needs a new carb, so if If I have to buy one anyway why not make it a 3hp! Not sure if they tune the exhaust differently or if it's just jetting. I know that normally it's not worth it to do on most engines. But I am just buying it to play with, and then will probably give it to my brother....
Thanks....

 

[ondarvr]

It is NEVER just jetting.

 

[pvanv]

You need the complete carb for an MFS3.5

3GV032000M

CARBURETOR ASSY, F3.5B

$156.35

 

[b.gagnon]

Thats not too bad!
I got the motor for $100 and I think it's an 06-08!
I may try to clean the carb with him first. At worst I would be $250 into a 4-stroke that look somewhat new (my 2015 has more scratches)...

 

[frustratedboater]

One option to change the compression ratio. With a motor of that size, it really isn't worth it. The second consideration is to look at your carb. You want to push as much fuel through as possible and with the first step (comp. ratio), it will increase. You can also mill/grind your ports to allow better out-flow and easier inflow of your fuel. Option three, sell yours and buy a 3!
Going back to the carb:
Here is an interesting vid: https://www.youtube.com/watch?v=2unnzYPutKQ...

 

[b.gagnon]

Im not looking to get that involved....:lol:
Was just wondering if it were as simple as changing the carb like the old 9.9-15hp evinrudes..
What ever I do, I need to keep it reliable. My brother knows nothing about engines!
If I am successful cleaning the carb then it will stay as a 2.5...If I have to buy one I will try for a 3.5 carb.

 

[funk6294]

If we are talking about a .5 horse increase I would just change the vinyl number to a three and be done with it. I doubt you would even notice the performance difference and it's quite likely the difference is nothing more than marketing.

 

[b.gagnon]

I actually meant to say 3.5hp....so it would be a 1hp gain!

 

[Sea Rider]

The question is : were both 2.5 & upgraded 3.5 versions tested at wot with a GPS and tach to know you have gained one full HP increase along better top end speed than when running at 2.5 HP ? Although you can buy 3.5 parts, sometimes 3.5 carb internal fuel passages are wider than 2.5 carb, if so, mods won't work as expected and that will make a notorious performance difference.

Happy Boating

 

[TOHATSU GURU]

Like Paul said. It requires a complete carb. There is no modification to the 2.5 carb that will result in it allowing the engine to reach 3.5 hp.

 

[b.gagnon]

Well...
I took the carb apart today (filled with gell) cleaned it ....Started 1st pull and ran great!
Seeing that it does not need any parts, it will live the rest of it's life as a 2.5hp!
Does anyone have any idea how to tell what year it was made? The freeze plug says030088xh
The motor looks to be in very good shape almost new ... The decals look like my friends 06 30hp tohatsu. It took 20min to fix and I paid $100. I wish I had found this before I paid $900 for my 3.5hp Merc!
Thanks...

 

[pvanv]

Well...
I took the carb apart today (filled with gell) cleaned it ....Started 1st pull and ran great!
Seeing that it does not need any parts, it will live the rest of it's life as a 2.5hp!
Does anyone have any idea how to tell what year it was made? The freeze plug says030088xh
The motor looks to be in very good shape almost new ... The decals look like my friends 06 30hp tohatsu. It took 20min to fix and I paid $100. I wish I had found this before I paid $900 for my 3.5hp Merc!
Thanks...

2008.

 

[Sea Rider]

Congrats on the bargin purchase price, sometimes sellers don't know what they sell, that's best buy for any boater.

Happy Boating

 

[b.gagnon]

The sad part is that I bought it from a dealer!
The customer never drained the fuel, and our high quality fuel did the rest!
They must have quoted him more than the engine was worth to fix it....

 

[steelespike]

On you tube there is a 2hp jon boat that actually planes.I think the operator is just a kid.