Tachometer

Arty

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Feb 12, 2015
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A while back, I decided to add a tach to my bike, so I ordered a "Whizzer" tach online, and modified it to work on my bike. The wiring is fairly basic -3 wires for the movement - hot, ground, and signal, and two for the tach light - hot and ground. You need a 12v battery supply for it to work - I'm using a rechargeable lithium ion.
For the signal (trigger) I used the hot wire to the CDI.
To mount it, I had to fabricate a custom mount, and cut apart a stainless steel soap pump for the case.
 

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zippinaround

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Aug 4, 2013
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or you can buy super cheap ones with that powers itself and just hooks up to the sparkplug only cost 5€ and no modifying or messing about , mine is still on its way but should be here soon hopefully
 

Arty

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Feb 12, 2015
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Yeah - it's on a 66cc, and seems accurate - but I have no point of reference to check it.
 

FurryOnTheInside

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Sep 23, 2013
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how exactly does one go about checking how accurate it is? fit it to something that already has a revometer?
If you have measured your roll out (the distance of one wheel rev while you're actually on the bike) you should be able use arithmetic to work out how many RPM it does at a given speed. With a speedo set up with the accurate roll out as the wheel circumference, make a little chart and tape to the stem/bar to check it on a ride. :)
 

zippinaround

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Aug 4, 2013
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If you have measured your roll out (the distance of one wheel rev while you're actually on the bike) you should be able use arithmetic to work out how many RPM it does at a given speed. With a speedo set up with the accurate roll out as the wheel circumference, make a little chart and tape to the stem/bar to check it on a ride. :)
whats the formula to change wheel rpm to engine rpm?
 

FurryOnTheInside

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Sep 23, 2013
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whats the formula to change wheel rpm to engine rpm?
I'll use some nice round figures* for example but you must measure actual roll out.

60km/hr = 1000m/min
Divide by
2m rollout*
=500 wheel RPMs
=500 rear sprocket RPMs
Multiply by
sprocket reduction 4 (10t:40t*)
= 2000 drive sprocket RPMs
Multiply by
internal reduction 4.1 on the 2stroke
=8200 RPM @ 60km/hr

(8200÷ 6 ) x 5 = 6833.3 @ 50km/hr
(8200÷ 6) x 4 = 4555.5 @ 40 km/hr
Etc.

:)
 

KCvale

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Vendor
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Apr 18, 2010
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3,518
I just use these.
https://www.amazon.com/TMS-Digital-Tachometer-Yamaha-Kawasaki/dp/B0049IFX56/ref=sr_1_3?s=automotive&ie=UTF8&qid=1474735032&sr=1-3&keywords=tach+and+hour+meter

$10 and works with 2 and 4-stroke engines (read the manual to set it).
It has an internal battery so just one wire coming out you just wrap arond the plug wire a couple times.
When the engine is off it displays the Total hours the engine has been on.
When the engine is on it displays RPMs.

Simple, cheap, and good for about a year.
 

zippinaround

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Aug 4, 2013
Messages
724
Well my tachometer arrived today took all of two minutes to set up ! Seems my engine revs all the way to 4000 rpm hahah man that's bad !
 
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