tiny tach accuracy

Discussion in 'Power it up with Electronics' started by topnative2, May 6, 2009.

  1. topnative2

    topnative2 Well-Known Member

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    Ques.    If a tiny tach is reading correctly at idle can one assume it is reading correctly at wot? Do I trust the tach?

    "Earballing it" it does not sound revved out but this my 1st 4str.

    the facts below:

    riverhawk b60
    merc 20hp 4 str.
    prop. 10p
    3500 rpm @ wot
    top speed 25mph (gps)

    ANY food for thought is appreciated :)
     
  2. Brett

    Brett > PRO STAFF <

    Mercury 20 FourStroke Specifications
    HP @ Prop 20
    kW @ Prop 14.9
    Max RPM (WOT) 5400-6100
    Cylinders 2 (in-line)
    Displacement (CID/cc) 21.4/351
    Bore & Stroke (in) 2.40 x 2.36
    Bore & Stroke (mm) 61 x 60
    Cooling System Water-cooled w/thermostat
    Ignition System CDI w/ electric spark advance
    Starting Manual or electric
    Gear Ratio 2.15:1
    Gear Shift F-N-R (Shift-in-Handle Tiller or Remote Control)
    Steering Tiller or remote
    Alternator Amp 12 Volt / 11 Amp
    Alternator Watt 139
    Trim Positions 6 or power tilt
    Shallow Water Drive Standard
    Exhaust System Through prop
    Lubrication System Wet sump
    Recommended Oil Mercury 4-Stroke Outboard Oil
    Oil Capacity 1.0 L / 1.1 Qt.
    Fuel Induction System 2-valve single overhead cam
    Remote Fuel Tank Standard
    Remote Fuel Tank (US Gal) 6.6
    Remote Fuel Tank (L) 25
    Shaft Length (inches) 15/20
    Shaft Length (mm) 381/508
    Dry Weight (lbs.) 115
    Dry Weight (kg.) 52
    Operator Warning System Low oil pressure / Over--rev
    Available Propellers Standard equipment
    CARB Star Rating 3

    Sounds like you're getting the right speed but the wrong rpm's based on the engine specs.

    Which model tach did you get?
    Appears to be reading half of the true rpms.
    A tach designed for a 1 cylinder engine
    and being used on a 2 cylinder engine
    might read only half the rpms.
     

  3. topnative2

    topnative2 Well-Known Member

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    the fac. sent a tt226r-2x w/ an L written next to the model number for the motor .I did it over the phone to eliminate mistakes.
    I did a total of 4 wraps plus 1/2 wrap at each end and trimmed
    Talked to the fac. and was advised I might need to put another wrap on it because of interference--just a "wittle" late  to do now!!!!!!!! ::)
     
  4. Brett

    Brett > PRO STAFF <

    Splice another chunk on, its an induction coil.
    The short length of the wire added shouldn't affect the electrical signal produced.
     
  5. topnative2

    topnative2 Well-Known Member

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    the instrc. say no-----but i like the idea and will do so
    thanks

    I thought I might go to a 9 pitch---good idea ofr bad?
     
  6. Brett

    Brett > PRO STAFF <

    Get your tach working right first.
    If you are in the power band 5400-6100 rpm
    then no need to change.
     
  7. topnative2

    topnative2 Well-Known Member

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    i do hate reality checks :)
     
  8. Kemo

    Kemo The world is flat....and shallow.

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    I just got mine yesterday from the factory. I ordered the TT226R-2C because that's what I thought I needed from reading the descriptions on their site. I received the same model as yours, the TT226R-2X with the hand-written "L" next to it, with a note on the packing slip that it was sent because it was the right one for my motor. I have a Johnson 15 2-stroke. I described my motor when I ordered it. I don't know what the difference is, but assume the factory knows best. Going to install it this weekend and try it out. Glad I saw this post, so I won't be trimming anything off until after I test it. I'll let you know how it works.

    Kemo :cool:
     
  9. topnative2

    topnative2 Well-Known Member

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    sounds like i am the ginny pig [smiley=dancing-smilie.gif] [smiley=shucks.gif]

    adjustment was to be done one wrap at a time

    await the results with great anticipation ;D
     
  10. Tom_W

    Tom_W Well-Known Member

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    I've never seen a Tiny Tach installation but if it is sensing spark plug firings then it shouldn't be the same part number for a 2 stroke and a 4 stoke - right?

    Tom W
     
  11. Brett

    Brett > PRO STAFF <

    Some engines fire the plug for the cylinder on every rotation of the flywheel.
    Others fire it on every other rotation, so half the number of rpm's would be read.
     
  12. Kemo

    Kemo The world is flat....and shallow.

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    Sounds like the tach factory thinks his 4-stroke fires every time. I'd question the motor factory on what that particular 4-stroke does.

    Kemo :cool:
     
  13. topnative2

    topnative2 Well-Known Member

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    are we having fun yet?
    ok --- the tt is showing proper rpm at idle ---does that not blow out the firing theory???????????

    does the fact that I  am 1500-2000 ft up make a difference ;D ::)

    this is one awesome site wish I knew about it when i was still a flatllander

    thanks
    ken
     
  14. Brett

    Brett > PRO STAFF <

    Proper idle rpm, hmmm, how do you know? By ear?
    500 rpm or a 1000 rpm? Idle speed, I dunno...
     
  15. topnative2

    topnative2 Well-Known Member

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    at idle the engine is in the zone according to the manual and the tach'''

    so..................

    lets keep the brain waves going-----that way if i have to call the fac. again i will have the collective i.q. behind me---meanwhile i need to get some wire and good weather for the test of previous fac. correction info and bretts splice idea

    KEMO----waiting to heart on ur install ;)
     
  16. noeettica

    noeettica Well-Known Member

    In My Opinion I would go with an 11 Pitch But I am Basing that on my 15 Horse Yamaha I run a 10.5 or 11 but by X what I would have to check the prop box

    Dave

    At Least i can hear when the Yamaha hits the rev Limiter ... Then go up one Pitch LOL
     
  17. topnative2

    topnative2 Well-Known Member

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    FYI>>> emailed the fac. and was advised the unit sent is correct for multi-cyl. outboards ----the :L: stands for a light fliter put into the unit to mitigate interference--
    hmmmm!
     
  18. Kemo

    Kemo The world is flat....and shallow.

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    Sorry, didn't get a chance to do my TT yet.  Sometimes I get a chance to do other stuff (for money) and I have to take advantage of it.  Hope to get back to the boat tomorrow.

    Kemo   :cool:
     
  19. Brett

    Brett > PRO STAFF <

    I wonder how you'd check your tach-uracy?    :-?


    found it...

    http://www.cadvision.com/blanchas/54pontiac/tach.html
     
  20. topnative2

    topnative2 Well-Known Member

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