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Piranha ignition and tach reading low  Rate Topic 
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 Posted: 06-19-2021 02:11 pm
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tallyhoe
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This is an older electronic ignition and I can't find any info on how to adjust or diode the beast to read correctly. Has anyone used/kept their Piranha spark box?

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 Posted: 06-19-2021 04:15 pm
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subwoofer
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Stock Smiths tach? Those are current triggered and a source of problems. Get one of the RVI to RVC tach conversion boards and remove a source of annoyance from you car: https://spiyda.com/smiths-rvi-rvc-conversion-board.html

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Joachim

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 Posted: 06-19-2021 05:13 pm
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tallyhoe
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Thanks.
Jay

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 Posted: 06-19-2021 06:24 pm
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subwoofer
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The mechanism could probably do with a cleaning too, if it seems sticky. That could be the reason that tapping on it makes it come down. I didn't clean mine because I couldn't get the needle off, didn't want to risk breaking it.

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 Posted: 06-19-2021 07:29 pm
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tallyhoe
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I actually have to tap it to make it kinda work, but cleaning sounds like a good start.

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 Posted: 06-20-2021 03:51 pm
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DonBurns
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I tried doing the spiyda conversion, and failed. You have to remove the needle and mine was very resistant and I think I ended up damaging the mechanism. My speedometer was also not reading right. I replaced both with Speed Hut units, that you can custom order faces and bezels for to pretty closely match the original look. They work perfectly and I am happy I went that way. Speedo is by GPS so you can remove the cable to the transmission, which also simplified the W58 installation. Also way cheaper than estimates I found to rebuild the Smiths. I've kept them just in case I ever feel the need to reinstall the originals. Don't see why I would, though.

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 Posted: 06-20-2021 06:21 pm
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subwoofer
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You dont have to remove the needle, I chickened out on that because it felt stuck. Still made the conversion, no problem.

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Joachim

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 Posted: 06-21-2021 10:54 pm
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Tom Bradley
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There is an adjustment screw in the stock tachometer accessible via a hole in the back of the case. These guys tend to age and go out of calibration. Its a pain to adjust, though.

I also did the conversion to Spiyda without removing the needle, but I did not think it was easy at all.

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 Posted: 06-22-2021 06:32 am
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subwoofer
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Hehe, I should have added a "YMMV" after "no problem". I find soldering surface mount electronics easier that through-hole, particularly when modifying circuits. I guess it's just what I have the most experience with.

As for the stock tach, if I remember correctly there is an electrolytic capacitor in there, that one will have nowhere close to it's original capacity by now. Also, the solder joints and the PCB are all likely to be well flaky by now.

If the needle sits at 0 and jumps into life when you tap the tach, I would say the problem is electronic. If it freezes or seems to stick in any random position and tapping it gets it going again the problem is mechanical - it needs a clean.

Tweaking the calibration screw will be very unlikely to improve matters.

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Joachim

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 Posted: 06-22-2021 12:30 pm
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tallyhoe
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It is dead until I tap it. Hopefully I will get to it this weekend. Thanks

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