25HP Nissan Question?

[tinman22]

I took my 2001 25hp Nissan 2-2troke outboard to a local dealer to get it serviced. I purchased the 30hp carb and was going to have them install that to get it juiced up a little. The mechanic I talked to said he would open up the jets a little bit and it would make it run "even faster". I have read on here a bunch and havent ever seen where that was done to these motors to enhance performance. Should I call and tell the guy not to mess with the jets, or does he know what he is doing? Please advise, I dont want this to be done if it wont help, or could possibly hurt the motor...

 

[Sea Rider]

Re: 25HP Nissan Question?

If you have changed for a 30 HP carb, why would the guy need to mess up with the jets ? sounds story for a profit...If the engine is same as newer existing Tohatsu 25/30 models, only need a 30 HP carb gasket swap for more air and in some cases depending on carb buttefly final position a + 5? timming advance to achieve 25? so to have 180? butterfly position at wot.

Happy Boating

 

[tinman22]

Re: 25HP Nissan Question?

If you have changed for a 30 HP carb, why would the guy need to mess up with the jets ? sounds story for a profit...If the engine is same as newer existing Tohatsu 25/30 models, only need a 30 HP carb gasket swap for more air and in some cases depending on buttefly final position a + 5? timming advance for the carb butterfly to be at 180? at wot.

Happy Boating

He was going to change it to a 30 HP carb and advance the timing per my request. He then added that if he made the jet bigger (I guess bore it out some), that it would give the motor "extra" juice on top of the gasket/timing change. He said he would do it for free, so I know he's not trying to scam me, but at the same time he didnt seem very knowledgeable about this particular motor. I dont want him to mess the motor up, but if it will help, Im all for it...

 

[pvanv]

Re: 25HP Nissan Question?

He was going to change it to a 30 HP carb and advance the timing per my request. He then added that if he made the jet bigger (I guess bore it out some), that it would give the motor "extra" juice on top of the gasket/timing change. He said he would do it for free, so I know he's not trying to scam me, but at the same time he didnt seem very knowledgeable about this particular motor. I dont want him to mess the motor up, but if it will help, Im all for it...

The only thing that would be accomplished by boring out the jet would be poor fuel mix ratios. Don't do it.

 

[Sea Rider]

Re: 25HP Nissan Question?

If both 2001, 25 & 30 carb models are the same as in newer versions, don't need to buy a new 30 HP carb, a matter of checking this, just swap for 30 HP carb gasket + 5? timming advance as seems your engines needs this to perform as a factory delivered 30 HP. The extra juice is at full throttle with advanced 5? timming compared to a restricted carb gasket/20? timming advanced 25 HP older model.

Happy Boating

 

[tinman22]

Re: 25HP Nissan Question?

My main question, is after changing the carb gasket and the timing....will messing with the jet help or hurt the performance of this motor. Im guessing dont do it?

 

[pvanv]

Re: 25HP Nissan Question?

My main question, is after changing the carb gasket and the timing....will messing with the jet help or hurt the performance of this motor. Im guessing dont do it?

The jet matches the throat of the venturi. Don't alter one without changing the other, or you throw the mixture off. I'm guessing you aren't going to setup a CNC mill to re-cut the carb body and nozzles -- and that you probably don't have the appropriate end mill to open up the jet (a regular drill bit will cause weird swirl marks inside the jet, leading to odd fuel delivery), so my personal recommendation is to not bore the jet. If this is an M25C3 with serial of 50039 or higher, I believe the 30 uses the same carb, so no new carb needed, BTW.