How to install an electronic tachometer on a CDI ignition

tdkrantz · 05-01-2010, 12:38 PM

How to install an electronic tachometer on a two cylinder, four stroke engine with CDI ignition.

I received my electronic tachometer yesterday and went to install it and realized that I had two coils instead of one. I tried hooking it up to one of the coils but that didn't work. I was ready to give up when I decided to do a little research on bikes with a tachometer hooked up to a CDI ignition with two coils. You ether had to have a CDI with a tachometer terminal built in or buy an adapter to hook both coils up to the one tachometer input. I didn't have ether one.

The adapters run about $30 + shipping. Then you have to wait several days or more for it to arrive in the mail. So, I said the heck with that and made my own for free. The parts cost about a $1.00 at Radio Shack but I already had them in my parts bins. It takes two 100k ohm resistors and two 1N4007 diodes. The diodes keep the current from flowing back to the other coil and the resistors smooth out the signal and keep the tachometer needle from bouncing. Thats it. Here is the schematic.

FastDoc · 05-01-2010, 01:13 PM

Will that work on a single cylinder Chinabike?

tdkrantz · 05-01-2010, 02:24 PM

Quote:

Originally Posted by FastDoc

Will that work on a single cylinder Chinabike?

I wouldn't think that you would need to add anything to a single cylinder installation. Just hook the green wire directly to the negative terminal of your coil and the other tach connections as shown in the diagram. I would do a little research first before shelling out any $$ for a tach. I should have looked @ my bike and did my homework before buying mine. Luckily it turned out ok.

There are also tachometers that just wrap a sensor wire around the spark plug wire to receive signals.

This one has a graphic tach & lots of other options like programmable indicator lights, speedometer, cyl/water temp, signals ...

http://trailtech.net/computers.html
Also available on ebay.

I almost bought one of these but I didn't think it would look too good on a cruiser. Plus its a bit out of my budget. :wink:

Weldangrind · 05-01-2010, 03:42 PM

Excellent report! What did you use to house the diodes and resistors?

waynev · 05-01-2010, 04:15 PM

Quote:

Originally Posted by Weldangrind

Excellent report! What did you use to house the diodes and resistors?

That diode and resistor would be pretty small, i'm guessing they were wired inline with a pc of heat shrink tubing over them to seal the deal. Nice work and i love the diagram.

tdkrantz · 05-01-2010, 06:01 PM

I thought about a pc board but didn't want to waist one. Actually I just paired them up and twisted the ends together and soldered 18ga wire ends on them w/connectors. I then shrink tubbed them individually and then shrink tubbed them as one unit. The end result is a "Y" shaped wire assembly that has a bulge in the middle. Fit neatly under your tank near your coils.

SpudRider · 05-07-2010, 03:21 AM

That is a very nice job, TD! Thank you for the excellent writeup.

Spud

CX500CAFE · 02-02-2017, 04:06 PM

First of all, sorry for digging up an old thread. But is there any chance you still have the diagram for how you did this? And if not I was hoping you could draw another one up, I am trying to put a modern digital tach on a motorcycle with cdi ignition.

Thank you.
Ryan

humanbeing · 02-02-2017, 07:10 PM

tdkrantz's bike is based from mid-90s JDM Rebel CA250. Don't know how's CX wired BUT https://item.taobao.com/item.htm?id=536139476392 pretty useful (had different Hz settings) .
The signal can grab from anywhere btw pulser & H.T. coil's input [H.t coil in/ CDi out / CDi pulse in / pulser out ]
Find the suitable point urself, somewhere that had the least eletctrical interference ...

davidstpek · 06-21-2018, 08:49 AM

Quote:

Originally Posted by tdkrantz

How to install an electronic tachometer on a two cylinder, four stroke engine with CDI ignition.

I received my electronic tachometer yesterday and went to install it and realized that I had two coils instead of one. I tried hooking it up to one of the coils but that didn't work. I was ready to give up when I decided to do a little research on bikes with a tachometer hooked up to a CDI ignition with two coils. You ether had to have a CDI with a tachometer terminal built in or buy an adapter to hook both coils up to the one tachometer input. I didn't have ether one.

The adapters run about $30 + shipping. Then you have to wait several days or more for it to arrive in the mail. So, I said the heck with that and made my own for free. The parts cost about a $1.00 at Radio Shack but I already had them in my parts bins. It takes two 100k ohm resistors and two 1N4007 diodes. The diodes keep the current from flowing back to the other coil and the resistors smooth out the signal and keep the tachometer needle from bouncing. Thats it. Here is the schematic.

Why can I not se diagram??

Weldangrind · 06-21-2018, 12:04 PM

The diagram was posted in 2010 and the original hosing site may be gone. That's why it's always best to upload pics directly to the forum.

humanbeing · 06-21-2018, 05:44 PM

Quote:

Originally Posted by Weldangrind

... the original hosing site may be gone...

The domain name resembles that username & available at this moment for ~$13

Troy · 05-05-2019, 01:48 PM

I'm back ... 9 yrs later.

Here's the diagram:

RKG83 · 05-06-2019, 06:39 AM

Y’all still have an open radio shack? That’s awesome

05-01-2010, 12:38 PM	#1
tdkrantz Join Date: Apr 2010 Location: USA, Virginia, Radford Posts: 50	How to install an electronic tachometer on a CDI ignition How to install an electronic tachometer on a two cylinder, four stroke engine with CDI ignition. I received my electronic tachometer yesterday and went to install it and realized that I had two coils instead of one. I tried hooking it up to one of the coils but that didn't work. I was ready to give up when I decided to do a little research on bikes with a tachometer hooked up to a CDI ignition with two coils. You ether had to have a CDI with a tachometer terminal built in or buy an adapter to hook both coils up to the one tachometer input. I didn't have ether one. The adapters run about $30 + shipping. Then you have to wait several days or more for it to arrive in the mail. So, I said the heck with that and made my own for free. The parts cost about a $1.00 at Radio Shack but I already had them in my parts bins. It takes two 100k ohm resistors and two 1N4007 diodes. The diodes keep the current from flowing back to the other coil and the resistors smooth out the signal and keep the tachometer needle from bouncing. Thats it. Here is the schematic.
	0

05-01-2010, 01:13 PM	#2
FastDoc Join Date: Mar 2009 Location: Southeastern Washington desert Posts: 14,761	Will that work on a single cylinder Chinabike? __________________ Happy to serve.
	0

05-01-2010, 03:42 PM	#4
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	Excellent report! What did you use to house the diodes and resistors? __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	0

05-07-2010, 03:21 AM	#7
SpudRider Join Date: Jul 2008 Location: Idaho Posts: 25,054	That is a very nice job, TD! Thank you for the excellent writeup. Spud __________________ Spud "Never argue with an idiot. He will drag you down to his level, and beat you with experience." Mark Twain 2015 Zongshen ZS250GY-3 (RX3) 2006 Zongshen ZS200GY-2 (Sierra 200) 2005 Honda XR650L 2004 Honda CRF250X 1998 Kawasaki KDX220 Mods made to my Zongshen ZS200GY-2: http://www.chinariders.net/showthread.php?t=6894
	0

02-02-2017, 04:06 PM	#8
CX500CAFE Join Date: Feb 2017 Posts: 1	CDI tach adaptor First of all, sorry for digging up an old thread. But is there any chance you still have the diagram for how you did this? And if not I was hoping you could draw another one up, I am trying to put a modern digital tach on a motorcycle with cdi ignition. Thank you. Ryan
	0

05-01-2010, 06:01 PM	#6
tdkrantz Join Date: Apr 2010 Location: USA, Virginia, Radford Posts: 50	I thought about a pc board but didn't want to waist one. Actually I just paired them up and twisted the ends together and soldered 18ga wire ends on them w/connectors. I then shrink tubbed them individually and then shrink tubbed them as one unit. The end result is a "Y" shaped wire assembly that has a bulge in the middle. Fit neatly under your tank near your coils.
	0

02-02-2017, 07:10 PM	#9
humanbeing Join Date: Mar 2008 Posts: 2,436	tdkrantz's bike is based from mid-90s JDM Rebel CA250. Don't know how's CX wired BUT https://item.taobao.com/item.htm?id=536139476392 pretty useful (had different Hz settings) . The signal can grab from anywhere btw pulser & H.T. coil's input [H.t coil in/ CDi out / CDi pulse in / pulser out ] Find the suitable point urself, somewhere that had the least eletctrical interference ... __________________
	0

06-21-2018, 12:04 PM	#11
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	The diagram was posted in 2010 and the original hosing site may be gone. That's why it's always best to upload pics directly to the forum. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	0

05-05-2019, 01:48 PM	#13
Troy Join Date: May 2019 Location: Virginia Posts: 7	Dual Coil Tach Hook-Up I'm back ... 9 yrs later. Here's the diagram:
	0

05-06-2019, 06:39 AM	#14
RKG83 Join Date: Jan 2019 Posts: 43	Y’all still have an open radio shack? That’s awesome
	0