More power

Discussion in 'Outboards' started by kenJ, Oct 18, 2010.

  1. kenJ
    Joined: Jul 2005
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    kenJ Senior Member

    I have a Nissan 2 stroke NS5B. I think I remember reading that all the single piston outboards are basically the same, power output is determined by the carb.

    Can I get more power out of the engine by putting a 6 or 8 hp carb on it?

    Looking at the parts diagrams it looks like the same carb body, can I just substitute the nozzles and jets from a 6 or 8 hp into my existing carb?

    Am I asking for trouble?
     
  2. tunnels

    tunnels Previous Member

    Simple if you want more power buy a bigger motor !! :confused: Whats the point of spending loads a dosh JUST to get another 2 hp ??
     
    Last edited: Oct 23, 2010
  3. powerabout
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    powerabout Senior Member

    no you need a bigger carb assuming that is how they engines went from 5 to 6-8hp
     
  4. Submarine Tom

    Submarine Tom Previous Member

    Ken,

    Looks like you might need to research this question elsewhere.

    Where did you read about the larger carb option?

    Where would you get said carb? They may have the info you're looking for.

    -Tom
     
  5. PAR
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    PAR Yacht Designer/Builder

    All depends on the "engine family" you outboard is from. In most cases you can upgrade to the top output for the engine family with off the shelf parts, like jets, venturis, timing, etc. If on the other hand you have an engine at the top of the output end of the family it's in, then you have to rely on classic hot rodding tricks to get more power. In you case and assuming my memory still works, the Nissan 2 NS5B is a three output engine family, a 4, 5 and a 6 HP version. So, with some minor changes, which I haven't looked up, you could increase the engine output by about 18%, which is fairly good considering you'll just be bolting on stuff.

    The question comes now, how much do you want from this little engine? The easiest way to proceed is to check the engine specs with the other engines surrounding it. I'm not completely sure what the difference between the A and B series are, but it might be worth a check.
     
  6. kenJ
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    kenJ Senior Member

    Thanks, I'm just looking for a bit more power, the dink won't quite reach a plane with 2 people on board. Guess I'll start looking for a 6hp carb off a junked motor.
     
  7. PAR
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    PAR Yacht Designer/Builder

    I don't think you need a new carb, just a main jet and some timing. I would start by taking the main jet up two sizes and advancing the timing a couple of degrees. The other options are to get the tune up specs and parts replacements guides and compare the differences. In all honesty, this isn't rocket science, but standard methods for getting more from an engine. Do your research on the engine family differences, then toss in the practical hop up tricks and you can get more then 6 HP. De-"flashing" the carb and air/duel delivery passages, port matching, entry and exit relief, etc. all can improve engine output.
     
  8. ondarvr
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    ondarvr Senior Member

    Assuming the jetting is correct right now, changing jets will not increase the power, only increase the chance of carbon build up and poor running.

    Jets are changed due to changing other components, larger carb, porting or exhaust. Sometimes you can change components and increase HP, on a couple of motors its a throttle limiter that needs to be removed, but typically the number of components needed for the increase total far more than what it would cost to just buy a bigger motor. You can check the parts breakdown for your year motor and see what's been changed by the factory to give it a higher rating.

    There is also a fudge factor for HP ratings, so many times the difference in HP isn't as big as what the sticker on the cowl may say. They may make a 2 and 3 HP model, the 2 may produce slightly more than 2 HP and the 3 may produce slightly less than 3 HP, this is done to reduce the cost of production and still have an outboard that meets the HP rating of more small boats. This results in people complaining that after installing all the new parts there is little or no increase performance.
     
  9. CDK
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    CDK retired engineer

    Only if the present carb is clearly undersized (narrower than the intake manifold) replacing it may make a difference. There may also be a restriction ring that you can remove to get more power.

    A larger main jet and advancing the ignition like PAR said will quickly tell you if there is potential for more power.
     
  10. powerabout
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    powerabout Senior Member

    there has NEVER been a production outboard that had more power than any other by a jet and timing change.
    I dont know where this wives tale came from?
    Are you trying to say the guys who tested them made mistakes?
     
  11. CDK
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    CDK retired engineer

    No, powerabout, I do not think so. But there are commercial reasons to sell the same engine with different output at different prices.

    I have a 9.9 HP Mercury 2 cylinder, labeled as 6 HP. They didn't even bother to put an insert in the intakes, just a long adjustment screw with a plastic sleeve around it to keep the throttle valve from opening more than 45 degrees.......
     
  12. tunnels

    tunnels Previous Member

    The older evinrude 9hp and 15 hp were the same motor just the 9hp was restricted , so a change of carb and the plate below and your 9 is a 15 hp !:)
     
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  13. PAR
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    PAR Yacht Designer/Builder

    Absolutely correct, but also out of context. I have a 20 HP Johnson now doing duty as a 30 HP with a few part changes 4 or 5 jet sizes and 7 degrees of advance. The engine cover still says 20 HP, but it was at the low end of the engine family, so it had the room to expand.

    The bottom line still is research and hot rodding if desired. I've never seen a stock engine that I couldn't get more out of, in some cases a lot more.
     
  14. powerabout
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    powerabout Senior Member

    looks like we all agree for a stock production as sold engine (was what I meant,sorry)
    Cheers
     

  15. ondarvr
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    ondarvr Senior Member

    Par, your original post said to change the jetting and timing, changing a few other parts makes it a totally different situation. Changing other things requires the change in jetting.

    Tunnels, there was only a short time span when OMC 9.9s and 15s were identical except for the carb, for most of their history it has been several different components that combined to make the increase. Even then people would complain that after installing all the parts there wasn't as much of a performance difference as they expected.
     
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