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Thread: 08 gsxr with long acre tach don't read right

  1. #1
    Senior Member harley's Avatar
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    08 gsxr with long acre tach don't read right

    Says it is 650 at an idle the whip I got had a wire spliced in one of the coil pack wires I thought the tach was set for the wrong motor but it's not does anyone use a longacre tach on there's if so how did u wire it after I got done racing I hit recall to see my max rpm it said 6850 it's def wrong

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    Re: 08 gsxr with long acre tach don't read right

    Can you change the settings on your tachometer?

    Your wiring is correct but you need to change the settings.
    You should set the tacho for 2 cylinders to get the correct RPM readings.

    On a four stroke car engine with a single coil the tacho gets two pulses from the coil in four strokes or two revolutions of the engine.
    On a four stroke engine with a coil for every cylinder the tacho only sees one pulse from the one coil every four strokes or two revolutions.
    Therefore you need to "fool" the tacho to get the correct RPM reading
    Last edited by Roy; 08-06-2016 at 03:50 PM.

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    Re: 08 gsxr with long acre tach don't read right

    Green wire - to “Tach” output on ignition box or to negative side of coil on non-electronic points systems. NEVER connect directly to a plug or coil wire!

    Black wire - to Ground Be sure it is connected to a solid ground. Many problems are caused by a poor ground.

    Brown wire - Power - 12 or 16 volt (connect so that it SHUTS OFF with ignition off).

    Red wire - Power (connect so it has power full time - NOT shut off when ignition is shut off)
    Accutech SMi tachometers
    Use only on 12 or 16 volt systems with negative ground. If mounted directly into firewall you must protect from exhaust radiant heat with an appropriate shield.

    To operate:
    Tach comes on automatically when the engine starts

    To recall:
    Push red "RECALL" button on lower left side. The pointer will recall highest RPM and hold that number (backlight flashes to indicate recall mode). Push again to resume normal tach operation.
    NOTE: You can push RECALL before going on the track and the tach will constantly display the highest RPM reached to that point without pushing RECALL again. It does not show active RPM once RPM drops below the highest point..Push RECALL to resume normal tach operation. This feature allows the driver to see what the RPM was on the track without having to push the RECALL button.

    To reset - erase max RPM:
    Push RESET button and hold 3 seconds to erase old RPM. Backlight flashes to indicate when done.

    To set number of cylinders:
    Push RESET and RECALL at the same time and hold 10 seconds (Note: After 5 seconds the LED will flash - see below. Continue to hold both buttons). After 10 seconds pointer will go to the number of cylinders - 4000 for 4 cyl, 6000 for 6 cyl, etc. Release both buttons. Then push either RESET or RECALL to change to the setting you want. After 5 seconds of no buttons being pushed normal function returns. Options are 2, 3, 4, 5, 6, 8, & 10 cyl. Factory set to 8 cyl.

    To Change High RPM warning light setpoints:
    There are 2 High RPM warning setpoints. On one the red LED is steady, the other the LED flashes. To change push RESET and RECALL at the same time and hold 5 seconds. Red LED warning light will flash. Release both. After a few seconds the LED will come on steady (not flashing) and the pointer will go to the current setpoint. This is the first setpoint - LED on steady. Use the 2 buttons to raise or lower the setpoint as desired. When you get the setting you want stop pushing either button. After 5 seconds the LED will start to flash. This is the second setpoint - LED flashing. Adjust as above. After 5 seconds of no buttons pushed normal tach function will return. Factory set to 8000 & 8500 RPM.
    THIS TACH IS NOT AN RPM LIMITER.

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    Re: 08 gsxr with long acre tach don't read right

    "Green wire - to “Tach” output on ignition box or to negative side of coil on non-electronic points systems. NEVER connect directly to a plug or coil wire!"

    This is correct when referring to the high tension coil wire between the distributor and the spark plug on a car engine with one coil and a distributor.

    On a engine with one coil for each cylinder you can splice into the 12 volt wire to one of the coils to get a signal for the tacho just as Harley has done.

    Harley's wiring is correct, but he needs to adjust the settings on the tacho to two cylinders to make the tacho to show the correct RPMs.
    Last edited by Roy; 08-07-2016 at 04:39 AM.

  5. #5
    Senior Member harley's Avatar
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    Re: 08 gsxr with long acre tach don't read right

    K thanks

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    Re: 08 gsxr with long acre tach don't read right

    Ok
    roy, Im asking because I don't understand. And I have seen that set up before. But if you splice into the 12 volt wire, how does the tach get a signal and from what.Theoretically, that 12 volt wire is connected to every other coil and all the way back to the ign. switch. And back to the battery if it is on.

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    Senior Member harley's Avatar
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    Re: 08 gsxr with long acre tach don't read right

    Not gonna lie I was stumped because from what little I know about coils wether I'm right or wrong someone can answer it better for me .most coils I have dealt with have a constant power to them and the crank sensor picks up a negative pulse which in turn fires the coil upon revolutions of the motor as for motor cycle engines it may be different or I am just totally wrong.i had disconnected the tach and taken it out before I had seen the post my tach does have the two cyl application on it I just didn't try it because I was smart enough to figure out it wasn't a two cylinder but what Roy says makes sense and it don't hurt for me to try it.i was just wondering why there wasn't a tach wire in the whips for them I am assuming the stock cluster has a tach on them there must be a better way to get the pulse beside tieing into the wire to the coil. And please don't take anything I am saying in a way of me trying to insult anyone I honestly am not and I thank you all for your input

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    Re: 08 gsxr with long acre tach don't read right

    Hello Rapid Roy,
    On a good ‘ole car with points in the distributor there is a 12 volt supply to the positive side of the coil (assuming a negative earth electrical system) and the negative side goes to earth via the points.
    Every time that the points open there is a surge in the high voltage side of the coil that powers the spark across the spark plug.
    The trigger wire for a rev counter is connected to the negative side of the coil so that the rev counter picks up a signal each time the points open to switch the current on and off.
    As you say on a bike engine with separate coil packs there is a 12 volt supply wire connected to every coil from the battery via the ignition switch and instead of the connection going back to earth from the coils via the points this is done through the ECU separately for each coil pack.
    Splicing into one of the wires from a coil pack to the ECU is the same as connecting to the negative side of the coil so the rev counter will get a signal each time the current is switched on and off to create the spark, but it only gets this this signal once every four strokes or two revolutions and therefor the settings on the rev counter must be changed.
    I hope this helps.
    regards,
    Roy

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    Re: 08 gsxr with long acre tach don't read right

    Hello Harley,
    The coils do have a constant 12 volt power to them and the connection to earth is switched on and off for each coil in turn by the ECU at times controlled by the crankshaft sensor.
    There is a signal from the ECU to the rev counter in the stock bike clocks but this may not be shown on the wiring diagram.
    On my car I have a standard clock cluster with the bike rev counter and I also have a digital rev counter with a max RPM recall wired in to one of the wires form the coil to the ECU. (set for a 2 cylinder engine to get the correct RPMs).
    I hope that this helps and please let me know if it works okay when you try this setting on your car.
    Regards,
    Roy

  10. #10
    Senior Member harley's Avatar
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    Re: 08 gsxr with long acre tach don't read right

    Thank you I will update ya

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