40 hp yamaha

Discussion in 'Bubba's Outboards' started by mitchell, Jan 28, 2006.

  1. mitchell

    mitchell New Member

    Messages:
    10
    State:
    Kansas
    my dad has this on a pontoon boat. the problem is when you give it full throttle it doesn't seem like its getting the max rpms. the motor just doesn't seem like it is running as fast as it should. any suggestions would be great.
     
  2. Bigun

    Bigun New Member

    Messages:
    234
    State:
    Burnet, TX
    Assuming that everything is right with the motor the prop and the load need to be matched. They proped my 24 ft pontoon where it only turns 5200 rpm at max throttle. This is running about 23mph. There is a limiter that is somewhere around 6000 rpm. A good mechanic will cost you about $100 to run check it in the water. You will know where things really are.
     

  3. Rockjumper

    Rockjumper New Member

    Messages:
    358
    State:
    Parker,Pennsylvania
    Drop prop size. Some dealers will let you try different sizes. A good dealer maybe able to tell ya what size you need. I think you are pushing to much water with the prop and can't acheive the RPM's. Good for power, but you may need to down scale some to gain the RRRRR's. You will gain speed plus have the power you need. Just my 2 cents.
     
  4. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    When was the last time it was serviced.and what year is it and do you have a tach on it and what rpms is it turning at wot.
     
  5. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Biggun what size motor are you running. 5200 sounds a little low to me.

    should be 5500 to 56 or 5700 but I need to know the engine size to determine this.
     
  6. jtrew

    jtrew New Member

    Messages:
    4,404
    State:
    Little Rock, AR
    Also, there's a difference between a speed prop and a power prop. You'll get better performance on a 'toon with a power prop.
     
  7. oldprowler

    oldprowler New Member

    Messages:
    321
    State:
    Mannford, Oklahoma
    mitchell: Its almost impossible to tell the RPMs of a boat motor without using the tach and without knowing the prop size and what the motor is taching at WOT real hard to tell if the rev limiter is set correctly or if you could benefit by changing the prop.

    My 40 yamaha did need to be re-propped from the factory but I don't remember what prop was on it. I am now running a 12 1/4 x 9, WOT tach is 5500 RPM. It is mounted on a 20ft pontoon and my max speed is 17.3 mph measured with GPS. At 3700 RPM the speed is about 14 (I don't remember exactly). My point is there is not a lot of speed gain during the upper 2000 RPM, at least on my pontoon. I do not have a fuel flow meter so I cannot pinpoint exactly the most effecient throttle setting but I would suspect that I am much more fuel efficient at or near the 3700 RPM
     
  8. Bigun

    Bigun New Member

    Messages:
    234
    State:
    Burnet, TX
    Bubbakat This is on a 100 hp 4 stroke Yamaha. This is probably too slow and kind of like lugging the Engine. This was the way the dealerships owners son suppossidly set it up. In his difence we have probably added quite a bit of weight since this was done. I mentioned this to the owner and he stated that it should be trning more rpm's. Thinking about a stainless prop but I will try a different pitch Aluminum before making the plunge.
     
  9. Mr.T

    Mr.T New Member

    Messages:
    2,553
    State:
    MO
    The dealer told me to keep my new 60hp Yamaha 4-stroke propped so it would turn about 6000 rpm at WOT - says it needs to be between 5700 and 6000 at WOT.

    The prop he installed is a little bit shallow on pitch, which allows the engine to turn about 6200 RPM. He says we can play with some different props till I find the right combination. Once it warms up a bit, I'll take him up on his offer.
     
  10. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Have him put you a cupped one on the same size and it will give you the range you want and good bite and good fuel miage.
     
  11. mitchell

    mitchell New Member

    Messages:
    10
    State:
    Kansas
    I think his tac is broken. I don't know what prop he is running but i check into that on my days off. thanks to everyone for your advice. H ave only been a member for a few days and I think this is the best bunch of guys and gals there are.