Tachometer interference
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
Likes: 7,968
From: poway
I've probably gone through 8-10 tachometers on different evos. All had the Dyna 2ki ignition which has a pink wire for tachometer. The only tachs that didn't wobble up and down a few hundred rpm were the Autometer and the custom chrome Japanese made FXR tachs.. The Taiwanese ones from drag, custom chrome and other places all wobble.. IMO it's has to do with the irregular firing order on the motor and crappy software implementation inside the tach. I suspect that the tack tries to measure the time between 2 pulses (1 period) or some other odd number of periods. As a results the depending on the which cylinder starts the sample the period changes and calculated RPMs is off... The tack wants to see 1 pulse per rev.. Timing between pulses is not the same.
The bike on my bobber has the issue as it now has a small Drag tach.. Bike kills the tach and speeds with great regularity so I'm not going to try a autometer.. Drag Tachs are like $60 where an autometer is like $250.
The bike on my bobber has the issue as it now has a small Drag tach.. Bike kills the tach and speeds with great regularity so I'm not going to try a autometer.. Drag Tachs are like $60 where an autometer is like $250.
Club Member
Joined: Apr 2011
Posts: 5,776
Likes: 7,811
From: SE Louisiana
Believe it or not I've seen poor stator output cause this issue as well doing AC test on your stator at idle should be around 13 to 16 volts AC and then do it at 2000 RPM should be 30 to 33 volts AC.. if that tests good check your voltage regulator..
But always check the coil as well 2.6 to 2.9 ohms on the primary side.. 10000 to 12,000 ohms on the secondary
But always check the coil as well 2.6 to 2.9 ohms on the primary side.. 10000 to 12,000 ohms on the secondary
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,006
Likes: 7,541
From: Poolville
I've never checked AC at the battery on a bike before, what would he be looking for? What values?
HDF Community Team
Joined: Dec 2005
Posts: 5,374
Likes: 2,570
From: NC USA
That's checking with a good, fully charged battery, under load (headlights are enough) and revved to 2000rpm. The meter used and the setting will make a big difference in getting a good (near correct) reading.
An oscilloscope is the only real way to test, but for these very basic charging systems a DVM is good enough. Vehicles with lots of electronics and sensors are a different story..
Cruiser
Joined: Apr 2020
Posts: 111
Likes: 45
From: australia
I have the exact same combo unit and had the same issue, cant remember what the proper term is but the signal to the Tacho is "dirty" you can add a resistor to the signal wire and calm it down. that's what i did. they are a very cheap purchase from an electronics supply store. i just cant remember what exactly the specs where i just bought a few different grades and soldered the to male/female connectors. i think they where like .5 of a watt. just Google "electronic tacho needle bounces around" and look for solutions that include adding a resistor to the signal wire. its a good idea to clean up all your connections and grounds as well.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
Likes: 7,968
From: poway
I have the exact same combo unit and had the same issue, cant remember what the proper term is but the signal to the Tacho is "dirty" you can add a resistor to the signal wire and calm it down. that's what i did. they are a very cheap purchase from an electronics supply store. i just cant remember what exactly the specs where i just bought a few different grades and soldered the to male/female connectors. i think they where like .5 of a watt. just Google "electronic tacho needle bounces around" and look for solutions that include adding a resistor to the signal wire. its a good idea to clean up all your connections and grounds as well.
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HDF Community Team
Joined: Dec 2005
Posts: 5,374
Likes: 2,570
From: NC USA
What would cause the needle to jump a little on my new tach, not a loose wire, not the tach cuz my old one did the same thing. 86 wide glide, Dyna S ignition. It's stable as can be at 3,000 rpm but below that is speratic. Something is is not right, size of the wire? Thinking outside the box.
My bike has the big FL dash with the Denso tach, uses a step motor and is smooth as silk plus my coil is stuffed up under the tank so I'm not gonna experiment.
But for y'all who have a coil on the left where its easy to get at, that'd be what I'd try next - plain old points style ignition condenser tied on at the feed wire to the tach.
Last edited by t150vej; Jun 6, 2023 at 04:51 AM.
