question on a 25hp Nissan 2 stroke

[Mysticwolf]

First off I would like to say hi to everyone, I just joint the fourm, and have a question. I have a 2005 Nissan 25HP 2 stroke That seems to run ok, but it will not get my boat up on plane (1448 Tracker) , it starts up good, idels goods, but when you give it full throttle, it just dont want to go very fast, I have put a different prop on, a CMC power tim unit, and a set of dolphin fins to try and help it, but it has done nothing to help my problem, I am at a loss. I had a 15 HP Mercury that would out run this 25, and I had a 16' boat then. Any ideas on what to do next? beside burn it in a fire? Thanks

 

[Georgesalmon]

Re: question on a 25hp Nissan 2 stroke

Any idea of the WOT rpm? What did you change your prop from and to? Pitch of old and new prop?

 

[Mysticwolf]

Re: question on a 25hp Nissan 2 stroke

Any idea of the WOT rpm? What did you change your prop from and to? Pitch of old and new prop?

Im not sure what you meen by WOT, And I am not sure what pitch my props are, I changed them last year. I will have to go home after work and look. I talked to a Nissan dealer, and the prop I put on is what he recomended. The motor just seems like it dont want to wind out all the way.

 

[Sea Rider]

Re: question on a 25hp Nissan 2 stroke

That's a restricted horse, why don't you pass it to a 30 HP for peanuts and start from there testing (wot) wide open throttle rpm) with actual prop and a induction tach. There's plenty info on the subject. Must start buying a 30 HP carb gasket and swap it for the 25 HP model.

If tracker is heavier than previous boat used with the 15, you'll need max power out of that block & prop. Check prop body, there's a graven small number which is....?

Happy Boating

 

[TOHATSU GURU]

Re: question on a 25hp Nissan 2 stroke

Im not sure what you meen by WOT, And I am not sure what pitch my props are, I changed them last year. I will have to go home after work and look. I talked to a Nissan dealer, and the prop I put on is what he recomended. The motor just seems like it dont want to wind out all the way.

You need to take the engine into a mechanic to determine what is wrong with it, the application or the operation.

 

[Mysticwolf]

Re: question on a 25hp Nissan 2 stroke

Thanks for the input, I guess my best bet is to take it somewhere, but if I do swap out the 30 HP carb gasket do I need to do anything with the timing? The prop I had on when I bought the motor was a 9.9x11, and the new one I put on is a 9.9x13 went a little bigger because I carry a lot of weight in my boat during hunting season, but the motor runs the same empty or with everything in it, so I know that weight has nothing to do with it.

 

[TOHATSU GURU]

Re: question on a 25hp Nissan 2 stroke

Yes, you need to change the timing and that it a huge prop pitch difference. A 13 would have a very difficult time getting on plane. In addition, changing from one brand of propeller to another will throw off the pitch difference. So, this is probably an application issue.

 

[pvanv]

Re: question on a 25hp Nissan 2 stroke

I believe Elvin is right on the money. Odds are you went the wrong way by using a steeper pitch. The available props are 8.3, 9.3, 10, 11, and 12. There are also 13 and 14 pitch props, but they are for very light boats.

Yes, you can change the carb gasket and verify the WOT (wide open throttle) timing to get to 30 hp. Likewise, you will want to get a tach on the motor to see what WOT RPM you have. You are probably way over-propped, so that the motor is not getting up to its optimal torque band.

If these concepts seem daunting, get to a dealer who can help you determine your present RPM, and that will help you get the most out of your rig. If the boat is unusually heavy, it may not be possible to achieve plane, but you can get it dialed-in to work the best.

 

[Mysticwolf]

Re: question on a 25hp Nissan 2 stroke

I believe Elvin is right on the money. Odds are you went the wrong way by using a steeper pitch. The available props are 8.3, 9.3, 10, 11, and 12. There are also 13 and 14 pitch props, but they are for very light boats.

Yes, you can change the carb gasket and verify the WOT (wide open throttle) timing to get to 30 hp. Likewise, you will want to get a tach on the motor to see what WOT RPM you have. You are probably way over-propped, so that the motor is not getting up to its optimal torque band.

If these concepts seem daunting, get to a dealer who can help you determine your present RPM, and that will help you get the most out of your rig. If the boat is unusually heavy, it may not be possible to achieve plane, but you can get it dialed-in to work the best.

So, sounds like I need to go back to the 11 pitch prop, correct? That may help, but that is the main reason I changed it to begine with,Because my boat wouldnt get up on plane. Should I try a smaller pitch like the 9.3 or 10? I carry alot of weight in my boat this time of year duck hunting, with all the decoys I have, plus guns ammo and 3 of us in the boat, not sure what size prop I need, The dealer told me I needed a bigger one, that why I went with a 13. We dont need to go fast when going out to set up, or coming in, most of the time it is still dark out, but when we have to chase down birds on the water, its a PITA! I have a friend that nows his stuff about motors, Think I will chnge the carb gasket and have him help me rset the timming, what should it be? and any idea what the WOT RPM should be? I really appreciate all the help you guys have giving me so far!!! This isnt my first boat, but this is the first time I have had issuse like this.

 

[pvanv]

Re: question on a 25hp Nissan 2 stroke

DL a copy of your owners manual from tohatsu.com for specs, including idle and WOT rpm listings. You can also get a Factory service manual from any dealer, including me. Heavier boats require less pitch, not more.

 

[Mysticwolf]

Re: question on a 25hp Nissan 2 stroke

DL a copy of your owners manual from tohatsu.com for specs, including idle and WOT rpm listings. You can also get a Factory service manual from any dealer, including me. Heavier boats require less pitch, not more.

Well, I think I am going to put my 11 pitch prop back on until I get a new one, its smaller than the one on there now, so it should help a little. When I get a new prop, what daimeter prop should I get, 9.9 or 10 1/2 x 9? Is there a big difference in daimeter size? I want to see how that makes it run before I try and changing the gasket and having the timing rest.

 

[TOHATSU GURU]

Re: question on a 25hp Nissan 2 stroke

The diameter is meaningless. It's the pitch that counts due to the fact that you do not have a choice in diameter in the same pitch.

 

[pvanv]

Re: question on a 25hp Nissan 2 stroke

Elvin's 100% correct as usual!

The only time diameter has much effect is on very large, slow-rpm props, such as used on large sailboats. Get a test tach on the motor, see what you have with your 2 props, and that will help you extrapolate what the ideal prop will be. Still, there will be some trial-and-error to hit the exact "best" prop for your application.

While at it, verify the jack height (higher is faster, until you go too high and suck air). The rule of thumb is 1" above or below the transom bottom, but you may want to experiment to get the best height. Too deep, and the extra drag will slow you a lot. That dial-in will also require trial-and-error, as each rig is different.

Unless you are super-concerned about fuel consumption, (or if the boat isn't rated for a full 30 hp), there isn't any reason to not convert to the 30 hp configuration. 20% more power for almost no cost.

 

[Sea Rider]

Re: question on a 25hp Nissan 2 stroke

Some engines comes with timing factory adjusted to 20?, others to 25?, place forward gear and full throttle grip, check which example setting is your actual timing stoping at ? Adjust it to 25? if with 20? + carb gasket swap. Once you have this well set place a induction tach and check if inside min, max wot rpm parameters with both props. Stay with the one that gives slight passing middle min, max rpm. A 30 HP will better your boating needs.

Happy Boating

 

[Mysticwolf]

Re: question on a 25hp Nissan 2 stroke

Well, Not sure what I did, but we went out hunting today, I put my old prop back on (9.9x11 ) was a 13, I also put a 1 1/2 " spacer between the trim and transom and the boat ran better that it ever has, I was shocked, got us rite up an plane with NO hesitation, My Buddy added something to the gas also, dont remember what it was called, but its made for boat motors, helps clean the jets and carb, that may have had something to do with it, I am still going to buy A new prop, think I and going to go to a 9.9x9.3 and see what happens,I am going to send my 11 pitch prop in and have it rebuild and taken down to a 10 pitch, and the 13 pitch i am going to do the same, but take it down to a 11, that way I will have 3 different sizes to chose from. I still want to change out my carb gasket, talked to a dealer yesterday about it, and he told me that wouldnt work, that a 30 HP carb is bigger, but for the cost, I am still going to do it, I appreciate all the help you guys have gave me, I have learned a lot in a short amount of time, Thanks

 

[pvanv]

Re: question on a 25hp Nissan 2 stroke

Jacking the motor 1-1/2" may well be the key here. Check the relationship of the antiventilation plate to the bottom of the transom -- should be about even, or maybe a little above. Requires trial-and-error to hit the sweet spot.

Fuel stabilizers will slow fuel rotting, but they don't "boost" power in and of themselves. You will still want to idle the carb out at the end of the day, to reduce varnishing.

Once you have a tach on the motor, you will be able to dial-in the best prop pitch, as well as the best jack height. Get as close to the specified max WOT RPM with going over.

That dealer is mistaken. The same carb, 3P0032000M CARBURETOR ASSY, 25C3/30A4, is used on both motors. The hp difference is in the 5 degree timing difference and the restrictor plate gasket (just like nascar).

 

[Sea Rider]

Re: question on a 25hp Nissan 2 stroke

Yes that dealer doesn't know his bussiness well, don't waste money trying different size, or pitch props. Instead investing and throwing $$$ guessing the right prop buy a Tiny Tach which is just 47 $ shipped to your home, go for a wot spin as usually loaded and go from there selecting pitch, not prop size. There are many Tohatsu pitches to play with, but a tach is a must have installed to check engine rpm factory parameters at wot in order to pick the right pitch for your boat/engine combo.

Happy Boating

 

[Mysticwolf]

Re: question on a 25hp Nissan 2 stroke

Well after reading what you guys have said, I am not going to buy a prop, I just ordered a digital tach to check out the RPM's, as soon as I get it installed, I will take the boat for a spin and see where it is, Then I will turn it into a 30HP, for the money, I dont think I can go wrong. Thanks for all your help!!!

 

[Sea Rider]

Re: question on a 25hp Nissan 2 stroke

5 HP added to a 25 HP will make the difference and day, go straight for the 30 HP piece of cake with wipped cream conversion, place tach and go from there testing max rpm achieved at wot with usual boat load on ideal flat no windy waters...Tech rpm parameters : 25 HP: 5-6 K / 30 HP: 5,150-5,850 tested at wot.

Happy Boating

 

[Nitewolf]

Re: question on a 25hp Nissan 2 stroke

The diameter is meaningless. It's the pitch that counts due to the fact that you do not have a choice in diameter in the same pitch.

dia does matter on prop
up one pitch-200 rpm
AND up 1/4 inch on dia - another 200 rpm