Installing tach

Discussion in 'Bubba's Outboards' started by benelli101, Aug 7, 2007.

  1. benelli101

    benelli101 New Member

    Messages:
    27
    State:
    mississippi
    I recently installed a tachometer on my motor and fail to believe what it is saying. I have a 1542 Cajun Tunnel Hull Jon Boat with a 2005 40 h.p. Mercury 3 cylinder 2 stroke. It has a 10.75 X 15 Power Tech ss prop. Boat weighs #230 and the motor is #203. I weigh 185. So basically it is a lightweight set-up. Rpm's are at 4800 and 33 mph. I find it hard to believe that this 15 pitch prop is only turning 4800 rpm. Either way i need to be turning 5500 or so. The tach is set on 6P also which is what is called for on this motor. Or at least that is what i understand. Any advice would be greatly appreciated.
    Thanks,
    Keith
     
  2. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    If you can find some one that will let you use another tach to compare yours to would be great.
    Most likely why you aren't turning more r's is the fact that you are running a ss prop. Those ss props take a lot to turn and your boat being a tunnel hull makes it even harder to push.
    Now how far is the cavation plate up or down is the cavation plate to the keel. I would have to look but would you happen to remember what the max r's are for that 40?
     

  3. benelli101

    benelli101 New Member

    Messages:
    27
    State:
    mississippi
    The cavitation plate is setting at the top of the tunnel. The max rpm's is 5500. I am thinking of going with a CMC tilt and trim unit for the adjustability and for the 6 in. set back.
     
  4. jim

    jim New Member

    Messages:
    2,579
    State:
    Jacksonville NC
    Keith go to www.turningpointpropellers.com and enter your boat and engine data.You will get a recommendation.I will be surprised if you dont get a 12-13 pitch recommendation.Also do you have power trim and tilt? If not have you adjusted the motor to different holes on the mount.33mph isnt bad for speed with that boat but you should be turning more rpms for sure.:smile2:
     
  5. benelli101

    benelli101 New Member

    Messages:
    27
    State:
    mississippi
    No i do not have trim and tilt, but yes i have adjusted it in every possible way. The only thing i can figure is that maybe the dirty water generated by the tunnel is playing a part in it somehow.
     
  6. benelli101

    benelli101 New Member

    Messages:
    27
    State:
    mississippi
    Turning point propellers site recomended a 15 pitch.
     
  7. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    That tach set at 6p should be about right if you are running a 9 or 13 amp charging system. Take an ohm meter and set it on DC volts and check the voltage going into the batteries.

    Does it have a water cooled recitfier on it?
     
  8. benelli101

    benelli101 New Member

    Messages:
    27
    State:
    mississippi
    I'll have to check the voltage, and i'm not sure about the rectifier. How would i check the rectifier?