2006 Sportster aftermarket tach

[M1n1fan]

My ‘06 Sportster (155 -non SC) has an aftermarket tach, readily available on Amazon for PWCs, motorcycles etc. it has to be programmed for pulses per rev. Has anyone done similar with their 155 4TEC and knows what the pulse count setting (1-300) for this rev counter should be? I diddled with it today and ended up with a setting of 21 (IIRC) that sort of seemed reasonable under actual run conditions. But I cannot set it using idle revs because i dont know what it idles at. And an add-on rpm counter/run timer doesn’t yet work because it cannot sense spark pulses due to the coil atop spark plug arrangement on the 4TEC.

 

[ski-d00]

It will idle at 1800 rpms which is ECU controlled so I think you are off quite a bit. It fires once for every 2 revolutions.

 

[M1n1fan]

Thanks! I knew of the 1800 rpm ECM “setting” but honestly thought that sounded high. I can “adjust” the rev counter to read dam near anything by way of its “ratio” value. As is, with the ratio at 21 or whatever, the rev counter is reading in the neighborhood of 600-700. More jiggering required.

 

[ski-d00]

You need to like triple your setting. 1800-1900 is typical for boat idles.

 

[M1n1fan]

Thanks! Its either triple or third it. Seems like as i set the “ratio” lower the revs increased. Regardless, now i know what to shoot for.

 

[M1n1fan]

Update: dialed the rev counter in to 1800. IIRC, the final setting for this tach (Amazon aftermarket 85 mm motorcycle, boat….) is 5.3. Not sure how this relates to cylinders (3), cycles(4). But apparently the ECM sends pulses that when applied to 5.3 (or close enough) results in a reading of 1800.