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85 Maxim X750 Tach very sluggish

Discussion in 'XJ Technical Chat' started by Alberta KTM, Mar 11, 2019.

  1. Alberta KTM

    Alberta KTM New Member

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    One of the last things on my rescue rebuild is the sluggish tach. The bike runs excellent but the tach is very slow to respond to rpm changes. I don’t think I’ve ever seen it past 3K no matter what the rpms are. I’m sure the correct pulses from the coil are making it to the tach. But not 100% sure. Am I looking at taking the tach to a speed shop or is there anything I can do first that make fix this slow as molasses tach? Thanks
     
    Alberta KTM, Mar 11, 2019
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  2. Ryengoth

    Ryengoth Active Member

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    Make sure you don't have corrosion on the connectors and you have proper voltage from the rectifier. I don't know much about the electronic gauges and I don't have a set to look at it but I can say that PWM circuits can be diagnosed with an O-scope and a PWM generator. I've spent many hours hacking CANBUS and PWM signals on my GenCoupe project. I'll dig around for info on the gauge and circuit. If anyone has signal specs for the tach let me know.
     
    Ryengoth, Mar 11, 2019
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  3. Alberta KTM

    Alberta KTM New Member

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    I did a little research and I’m gathering a mid 80s tach on a Japanese bike is fairly universal in overall operation. Story’s of rusted or goop on the moving components inside the housing. As this bike sat in a farm yard uncovered for years, I’m guessing that’s more than likely my issue. Should change the thread title to How to open a tach without scratching it!
     
    Alberta KTM, Mar 11, 2019
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  4. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    k-moe, Mar 11, 2019
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  5. Toomanybikes

    Toomanybikes Well-Known Member

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    Spiders and cobwebs
     
    Toomanybikes, Mar 11, 2019
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  6. Alberta KTM

    Alberta KTM New Member

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    So I removed and opened up my tach yesterday. Much to my chagrin, it was nearly spotless inside. I manually moved the dial and it took a couple seconds to return to 0 from 8k. I shot a small amount of silicone spray at the spring and disk. Operated it 20 or so times. Moved a little less sluggish. I connected the lead and fired up the bike. It moves a fair bit free er but not like it should. If I crack the throttle and hold it to say 3 grand, it will get there in about 2-3 seconds whereas before it never went past 2k. So I’m moving in the right direction but it’s a ways to go yet
     
    Alberta KTM, Mar 12, 2019
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  7. Bilfknmury

    Bilfknmury New Member

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    I personally used mouse milk penetrating oil on mine. Applied it with a q-tip to the shaft and worked it back and forth quite a bit. After a bit of use riding the bike the tach works as advertised. I'm extremely happy with the results.
     
    Bilfknmury, Mar 13, 2019
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