up-rating my Nissan 25HP 4 stroke outboard

[marc_lindquist]

I just purchased a Nissan 25hp and want to uprate my motor to 30hp. I see that it is the parts as stated above. does it work? do I have to buy the 3 carbs or can I just change the Jets? Also if I just to the carb change, is there anything else I need to do to make the motor work? any assistance on changeout would be great!

 

[pvanv]

Marc,

This is a 9 year old thread; You really should start a new one.

What is your actual specific model? If it's NSF25A, you will need all 3 carbs. They use the same link rod. You cannot just change jets, or it will flood. If it's NSF25B, you would need an different ECU and air inlet (not cost effective).

 

[marc_lindquist]

I just purchased a Nissan 25hp NSF25A EPT and want to uprate my motor to 30hp. I see that it is the parts as stated above. does it work? do I have to buy the 3 carbs as shown in the parts diag on page 10, there are 2 different listings(25hp & 30hp) for each of the carbs:
Ref No's
5-1 Upper carb
5-2 Center carb
5-3 Lower carb
I believe these listings are for the WHOLE carburetor. Can I just change the 1-main nozzle, 2-jets and the link rod? Also if I just to the carb change, is there anything else I need to do to make the motor work? Anyone have experience with doing this? If you have, any experiences of difficulties would be helpful. When I do it i am going to try to make a video of the repair

 

[Scott Danforth]

welcome aboard

the easiest way to convert a 25hp to a 30hp is either spend a whole lot of money on a whole lot of parts, or sell the 25hp, add a little bit of money and buy the 30hp. (BTW, its cheaper, easier and faster to do the later)

 

[marc_lindquist]

From what I see it’s 550 for 3 carbs or 5 grand for new motor and I won’t get 4 for my motor

 

[Scott Danforth]

you have a used motor now. get a used motor

 

[GA_Boater]

See post #3 by pvanv. It was moved from the old thread.

 

[Sea Rider]

Probably more parts involved that just a 3 carb swapp, ECU for instance. More fuel, needs more time advance compensation and that's electronically controlled.. A matter to check both HP Spare Parts Manuals to figure it out.

Happy Boating

 

[marc_lindquist]

from what I have read in the book, it is only the 3 jets in the link rod for each carburetor is the only difference between the 25HP and the 30HP motor's. I have read that people have just switched out the carb's and it worked. my problem is that I haven't found any 30hp 4 strokes around here for the price of switching it over and if it is as easy as it looks. Thank you for your advice on what to do and if anyone has any other advice, I would love it.

 

[Sea Rider]

This post is pure tech speculation on my part as don't presently work with 4 strokes Tohatsu OB's. If both models happens to share exact same carb parts number which isn't known, there must be a form of restriction, mechanically speaking the 25 HP isn't opening all the carbs fully while the 30 fully does while the time advance is electronically controled on both.

So if the mechanical throttle restriction of the 25 HP was released and now adjusted to work with 30 HP throttle parameters a 30 HP needs more time advance to compensate the extra fuel intake the carbs are delivering, if not OB will not work properly, will probably tend to drown in unburned gasoline and bog down when at medium to full throttle.

Tohatsu used to post on their web page the specific tech data for each model, no time advance data is now available, will give us a clue it both works with same time advance setting, if so, probably is just jets or full carb swap to know. If not, it's an ECU and carbs swap costly investment.

Paul, the ball is entirely on your side...LOL!!

Happy Boating

 

[pvanv]

from what I have read in the book, it is only the 3 jets in the link rod for each carburetor is the only difference between the 25HP and the 30HP motor's. I have read that people have just switched out the carb's and it worked. my problem is that I haven't found any 30hp 4 strokes around here for the price of switching it over and if it is as easy as it looks. Thank you for your advice on what to do and if anyone has any other advice, I would love it.

No. The Carb Castings are larger on the 30's. If you swap jets, you will run so rich that the plugs will go black very fast. The link rod is identical. You need all three carbs. Period.

 

[pvanv]

This post is pure tech speculation on my part as don't presently work with 4 strokes Tohatsu OB's. If both models happens to share exact same carb parts number which isn't known, there must be a form of restriction, mechanically speaking the 25 HP isn't opening all the carbs fully while the 30 fully does while the time advance is electronically controled on both.

So if the mechanical throttle restriction of the 25 HP was released and now adjusted to work with 30 HP throttle parameters a 30 HP needs more time advance to compensate the extra fuel intake the carbs are delivering, if not OB will not work properly, will probably tend to drown in unburned gasoline and bog down when at medium to full throttle.

Tohatsu used to post on their web page the specific tech data for each model, no time advance data is now available, will give us a clue it both works with same time advance setting, if so, probably is just jets or full carb swap to know. If not, it's an ECU and carbs swap costly investment.

Paul, the ball is entirely on your side...LOL!!

Happy Boating

The ECUs are identical. The carbs for the 30 are larger, and have bigger jets. The link rod is identical.

 

[pvanv]

3R0032001M

CARBURETOR UPPER ASSY

$234.90

3R0032041M

CARBURETOR CENTER ASSY

$208.33

3R0032101M

CARBURETOR LOWER ASSY

$208.33

Your cost after discounts would be $588 plus freight.

 

[Sea Rider]

Paul, what would be the cost difference between a 25 & 30 HP OB ? Assume much less than buying a 25 and modifying it to a 30 HP investing $ 588 + shipping. Probably not cost effective as going straight for the 30 HP one.

Happy Boating

 

[marc_lindquist]

Thank you for the information. You saved me a bunch of anguish on trying to use the same carbs and getting very frustrated

 

[Sea Rider]

If planned using same 25 HP carbs and just swapping 30 HP jets, that would't work at all. Fuel passages and jets are wider on the 30 HP.

Happy Boating

 

[pvanv]

Paul, what would be the cost difference between a 25 & 30 HP OB ? Assume much less than buying a 25 and modifying it to a 30 HP investing $ 588 + shipping. Probably not cost effective as going straight for the 30 HP one.

Happy Boating

When new, the 30 is about 400 more.