Digital Tachometer - Harley Davidson Street Forum - Street 500 and 750
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post #1 of 12 Old 09-27-2017, 10:37 AM Thread Starter
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Digital Tachometer

Hello All,

I recently installed a Koso Digital Tachometer on my 2016 Street 750 by wrapping the Tachometer wire around the spark plug cable. This was secured in place using insulation tape. The pulse setting was set to 1 for a 4 stroke and 2 piston engine. However the RPM readings are way off and low when compared with the FP3 output. Idling shows about 700 and on 6th gear it moves to about 1300 RPM. Has anyone installed this tachometer and faced a similar problem and the method of resolution. I will be grateful for answers.
Thanks
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post #2 of 12 Old 09-27-2017, 02:18 PM
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I have a 2017 XG750 that has a tach and gear display; it usually reads around 1350 rpm when idling.
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post #3 of 12 Old 09-28-2017, 04:00 AM Thread Starter
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Thanks. 2017 has a built in tach doesn’t it. If it is aftermarket how have you installed it?
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post #4 of 12 Old 09-28-2017, 04:45 AM
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The Coil only Fires one plug at a time. Why a reading about 1/2 of the idle speed. Try a different setting. Had the same problem using a DVM on the Tachometer setting.

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post #5 of 12 Old 09-28-2017, 08:04 AM Thread Starter
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Thanks Tucsonmax1. I have currently set the pulse at 1 which is what the instruction manual states for a 4 stroke 2 piston engine. Should I go ahead and set it at 2 and check but then that is for a 4 stroke 3 piston engine. Will that make any difference?
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post #6 of 12 Old 09-28-2017, 12:16 PM
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I say it can't hurt to try but I'd call the manufacturer to see if they have suggestions. And yes, the 2017 750 has a built-in tach and (very useful) gear indicator display.
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post #7 of 12 Old 09-29-2017, 12:26 AM
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Since you're only looking at 1 cylinder, set it for 1 cylinder. If you used this on an 8 cylinder 4 stroke car engine (on the coil wire) you would be getting 4 pulses per revolution. However, some ignition systems spark each plug at the top of the exhaust stroke also, so you would get 8 pulses per revolution in that case.

I ASSUME Harley only sparks the top of the compression stroke, so you will get 1 pulse for 2 revolutions of the engine. That means the correct setting is 1 cylinder, 4 stroke is the correct setting. Just play with it until you get reasonable numbers-- common sense. You can't hurt anything by trying different settings.
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post #8 of 12 Old 09-29-2017, 01:24 AM Thread Starter
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Thanks a ton for all the support and yes as Buttersmooth mentioned there is no harm playing around with the pulse settings till the readings are in tolerable limits. Will check and post the information.
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post #9 of 12 Old 09-29-2017, 05:10 AM Thread Starter
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Once again Thanks to all. I checked out various settings and finally when I came a full circle to 0.5 the Tachometer was well within tolerable limits of the FP3 plus minus 10 on the counter. So it is working properly but I am curious to know why 0.5 when the instructions state 1 for a 4 stroke 2 piston engine. At 0.5 the RPM has doubled from 1.
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post #10 of 12 Old 09-29-2017, 05:16 AM Thread Starter
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Buttersmooth - you have nailed it. I responded earlier without going through the last part you have mentioned 4 stroke 1 cylinder making the pulse setting 0.5 and that gave the correct RPM output on the Tachometer.
Thanks again
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