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Thread: PET tach help

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    Yamaha artisan Cutlass's Avatar
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    PET tach help

    Ok, so I bought a used PET-2100 tach. My GP1200 is all in pieces but this tach is so neat I wanted to try it out on something. So I went over to my buddies house and tried it on his '83 Honda 250r 3 wheeler, a 2 stroke snowblower, a 25cc GoPed scooter, and my V8 Jeep. We cannot get get this thing to work well at all. I took it to work the next day and tried it on a '08 Escalade (one coil and wire per cylinder) and a wastespark Northstar V8 Cadillac Seville. This tach just doesn't read right it seems.
    Any tips? How sensitive to interference is this thing?We tried wrapping the wire around the plug wire as well as the clamp. We tried 2 stroke 1 cylinder mode for the 3 2 stokes we tried and all the 4 stroke settings for the 4 strokes we tried. Nothing worked. RPM always reads way off or kinda close, but when ever something is rev'd up the reading doesn't follow.


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    Yamaha artisan Cutlass's Avatar
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    yeah, I've ready checked that out. I believe I understand how to use the tach, but for some reason the results aren't working out. For the three 2 strokes we tried (the 3-wheeler, snowblower, and GoPed) we use the P21:42 setting which is for 2stroke/1 cylinder engines. The 3 wheeler read 4000rpm at idle (should be less them 2000), the Snowblower read 3800rpms which seemed like it might be ok but also sounded like it was a little more then that, the GoPed read around 4000rpm at idle and a quick rev got it up to 12000rpm...again might be right but the "sound" didn't seem to match the readout.
    The Jeep read 650 at idle(sometimes) but the dash indicated 800 rpm. We rev'd it to 2000rpm and the PET read 1200. REV'd to 3000 and the PET read 1400 rpm. Setting was P24:48. We tried P:41 also and it read @ 3500 idle.
    The Cadillac read similar to the Jeep. Idle might be close, but rev'd up not even close. Very erratic also

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    krispaintballz's Avatar
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    First off get rid of that clamp and wire crap and go to an electronic store and get som solid core wire around the same size as the hole on the pet tach. Then wrap the wire around all three plug wires multiple times as close as you can to the cdi box. Finally I like to zip tie around the wraps to keep them secure around the wire.

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    Yamaha artisan Cutlass's Avatar
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    Ok. Yeah I can try that. I didn't like the clamp or the way the wire wraped around anyways. Any particular reason I should be wrapping it closer to the CDI box, then the spark plug itself? So if i wrap all 3 wires, I should use P23:46 (2 stroke, 3 cylinder), right? But if I just wrap one wire, I should use P21:42 (2 stroke, 1 cylinder), correct? I'm just trying to get a good understanding of this. Seems like it shouldn't matter if I measure one cylinder or all 3 as long as the mode setting is correct. The piston moves up and down once and thats one crankshaft revolution.
    Thanks for the help so far guys!

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    Moderator beerdart's Avatar
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    Setting will depend on if the CDI is a wasted spark or sequential spark.

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    krispaintballz's Avatar
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    Quote Originally Posted by Cutlass View Post
    Ok. Yeah I can try that. I didn't like the clamp or the way the wire wraped around anyways. Any particular reason I should be wrapping it closer to the CDI box, then the spark plug itself? So if i wrap all 3 wires, I should use P23:46 (2 stroke, 3 cylinder), right? But if I just wrap one wire, I should use P21:42 (2 stroke, 1 cylinder), correct? I'm just trying to get a good understanding of this. Seems like it shouldn't matter if I measure one cylinder or all 3 as long as the mode setting is correct. The piston moves up and down once and thats one crankshaft revolution.
    Thanks for the help so far guys!
    Closer to the cdi box will give you a better signal. Also you have to remember it needs to be on the 3 cyl because there are three pickups at 120 degrees and the coils all fire at the same time. Wrapping it around all three gives you a better signal.

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    Yamaha artisan Cutlass's Avatar
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    So I think my GP1200 has 3 pickups spaced 120 degrees apart like Kris said. doesn't that make it sequential spark?

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    mudslanger's Avatar
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    Quote Originally Posted by beerdart View Post
    Setting will depend on if the CDI is a wasted spark or sequential spark.
    I believe you confused him lol. Wasted spark or (Dual Fire) Spark on compression and exhaust stroke in 4 stroke engines. Non Wasted Spark Or (Single Fire) Spark only on the compression stroke in 4 stroke engines. if you set the tac. to 4 stroke on a 2 stroke engine it will not work right. if you put the sensor wire on all three wires the sensor will pick up three pulses per revolution of the engine if all three coils fire at different times per 1 revolution. i would try setting to 2 stroke mode single cylinder and connect the sensor wire to 1 plug wire close to CDI box. if you dont get an accurate reading your tac. may be faulty.

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    Yamaha artisan Cutlass's Avatar
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    I made some progress today. I got the tach to work flawlessly on a Cadillac DeVille at work today. I'm getting some solid core wire this week for the antenna and I'm gonna head over to my buddies house to try the tach on his 3 wheeler and his Banshee atv.

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