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Howard Inough
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Pelle Offline OP
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In case someone finds this useful:

I started to install an electronic tachometer (Speedhut) and could not get it working. So I did a voltage test. With ignition on but engine off, my cheapish digital multimeter said 13.6 volts. With the engine running, the multimeter readings were unsteady, around 18 volts. I suppose that could suggest a failing regulator, but in this case the cause was: the spark plug. Switching to a resistor type plug, in my case a NGK BR6ES, the multimeter now showed a steady 14.6 volts with the engine running, and made the tachometer function as intended. And that is how I learned that non-resistor plugs can play tricks with an electronic tachometer and a digital multimeter.

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Not using resistor plugs or caps can also play tricks with modern regulators and digital volt meters.


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DOPE
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no [***].

i had somuch trouble withmy speedhut tach that i gave up.

and i did NOT run resiztor anything.

clearly further testing is indicated


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Been using a speedhut on the 650 race bike since day 1. It was great until I hooked up the dual plug head. The tech at speedhut thought it could be ignition interference so I tried resistor plugs, resistor caps and both plugs and caps but no joy. Open to suggestions.......

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...Hi Kevin; remember that magnetos do not like resistor plugs...or is other bike?
I will have that problem with the magneto and the motogadget speedometer that I have but not installed it yet...

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I screwed around with a Speedhut tach for a couple of years. They have a lifetime warranty on the electronics, so I sent it back in twice, but then I got tired of sending it back and gave up. I also engaged in extensive email dialog with the techs at Speedhut.

At first we suspected the problem was low-frequency noise in the power circuit, possibly due to coil "bounce", so I ran dedicated power wires to the battery (via the fuse of course, and a dedicated switch). This did not help, and the gauge crapped out again in short time.

There were some other problems with the bike, a failing battery, a dodgy ignition switch, a worn alternator rotor, and a failing coil, all of which I fixed before my third attempt with the tach. I did not go to resistor plugs or leads, but I did use shielded wire for the pickup.

The gauge worked for a little while and then failed again. My conclusion, or theory at this point is that the gauge cannot tolerate voltage fluctuations. The Speedhut unit is made for automobiles, not motorcycles, and the much larger batteries in automobiles provide a more stable voltage.


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Anybody using a digital speedo if so do they suffer similar problems, having a problem with my Smiths magnetic so thinking of replacing it with a digital speedo from www.digital-speedos.co.uk

Cheers Dave


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Pelle Offline OP
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Originally Posted by Mark Z
My conclusion, or theory at this point is that the gauge cannot tolerate voltage fluctuations.

Yes, I think the Speedhut gauge is sensitive to voltage fluctuations but I don't know if it will damage the gauge. In my case the non-resistor spark plug fooled my digital voltmeter (but not my analogue meter!) to register fluctuating and too high voltage, while the actual voltage was spot on and steady. I guess the gauge was confused in the same way.

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I have the legendary (speedhut) gauges on my norton and with 20,000 + miles no issues. the first 15,000+ with non resistor wires, plugs and caps. after switching over to a Boyer micro digital I now have resistor caps and wires to stop a kickback issue and still have NO issues with either gauge.


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I had a Speedhut tach on a 70 T120 Cafe job with a small battery, no problems..And on my 96 Ducati and the Buell that Kevn now owns.


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Its not voltage fluctuations that are the problem, it's electro magnetic interference.
If bikes had radios this conversation wouldn't happen


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Pelle Offline OP
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Originally Posted by Andy Higham
Its not voltage fluctuations that are the problem

Not in my case anyway, as the actual voltage was steady. For all I know, it was EMI that caused the gauge (and my meter) to act up. However, I don't think the Speedhut gauge would perform well with fluctuating voltage.

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A 100uf cap in parallel with a 0.1uf across the supply close to the instrument may sort t out.
BUT it pays to use screened pickup leads and resistor plug caps.

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The most simple solution:

Just get rid of the tach.

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Originally Posted by Irish Swede
Just get rid of the tach.

Well, I'm glad I didn't

[Linked Image from i.imgur.com]


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