Programing an electric tach

Jul 24, 2017
811
632
63
San Diego, Calif
Name
Joseph Gratteau
Boat
Valco Westcoaster 150'
I have a 40 HP 4 stroke Mercury (ELPT EFI) and bought a digital electric tach/hour meter. It asks how many sparks per revolution, as the sensor wire wraps around one plug wire. I am unsure of this answer. I am trying to see how the boat is propped-hoping to be around 6000 RPM at WOT. I have tried a few settings of sparks per rev. (1P1R, 2P1R..) but the tach numbers do not seem to match. Does anyone know how many sparks per revolution? Thanks in advance-
 

tuner

pysgotwyr
  • May 24, 2006
    1,418
    936
    Huntington Beach
    Name
    Steve
    Boat
    260 Mackinaw
    Four stroke is 1 spark for 2 revolutions. Some four stroke engines use a "wasted spark" ignition and will have 1 spark/revolution
     
    Jul 24, 2017
    811
    632
    63
    San Diego, Calif
    Name
    Joseph Gratteau
    Boat
    Valco Westcoaster 150'
    this one has 3 cylinders-I understand the 4 stroke vs 2 stroke concept, compression/ignition stroke, and a exhaust stroke. I do not know how many cylinders fire on a revolution. Do each (or all 3) fire for each revolution?
     

    tuner

    pysgotwyr
  • May 24, 2006
    1,418
    936
    Huntington Beach
    Name
    Steve
    Boat
    260 Mackinaw
    The number of cylinders does not effect the inductive tachometer, only the frequency of the spark plug wire it is attached to.

    Firing order is normally equally spaced by degrees of crankshaft rotation

    8cyl is 90*, 6cyl is 120*, 4 cyl is 180, 3cyl is 240*, 2cyl is 360*, and 1cyl is 720*
     
    Jul 24, 2017
    811
    632
    63
    San Diego, Calif
    Name
    Joseph Gratteau
    Boat
    Valco Westcoaster 150'
    So with this tach, it only lists a handful of programable options. Each choice is how many sparks per revolution. 1 spark for 2 revolutions is an option I will try. Thanks, I hope it works! Hard for me to conceptualize!
     
    Jul 24, 2017
    811
    632
    63
    San Diego, Calif
    Name
    Joseph Gratteau
    Boat
    Valco Westcoaster 150'
    I made the mistake of googling it, even more confused! I guess I will have to try all options, until I find an idle speed of 1100-1200 RPM. Thanks to all who shared the info!
     

    jayyyy

    I Should Upgrade My Account
    Oct 7, 2008
    1,033
    258
    NorCal
    Name
    jay
    Boat
    '04 Sea Pro 220 WA / 225 Honda
    I've been through that, ended up turning the adjuster with the engine running till it was accurate. It will be way off until you select the right pole number.
     

    GrabBass1

    GrabBass1
    May 12, 2009
    393
    98
    Menifee, CA United States
    Name
    Joe
    Boat
    2008 176 Sea Pro Center Console - GrabBass II
    My understanding is that this setting is related to the number of poles the alternator has.
    This table says to set the tach pulses to half the number of alternator poles so a setting of 6 would work for your engine. I have a Mercury 115 HP and 6 worked for me as well.
    Found this at https://www.marine-j.com/pdf/faria_tacho.pdf
    Hope it helps...
    1618671823508.png
     
    Jul 24, 2017
    811
    632
    63
    San Diego, Calif
    Name
    Joseph Gratteau
    Boat
    Valco Westcoaster 150'
    6 sparks per revolution? That would be a total of 18 sparks per Rev. (3 Cyls). I will check my SN, but it sure seems high! I should have tried all options during lobster season...waiting to pull pots.