Acewell tach wrong

Wired my acewell speedo up to my coil today like the instructions say. Instead of wrapping the wire around the spark plug wire, I wired it directly to the coil as is one of the options. But I'm getting what I think a tach reading of what is double my actual rpms. The acewell reads ~4000rpm while the old mechanical tach reads~2000 rpm at idle. I know the idle is how the jetting needs to be adjusted it wrong idle below that at the moment. Any help greatly appreciated!! The bike is a 74 cb750 running dynatek 3ohms coil and dynatek ignition.
https://youtu.be/vqtqjTumSZ8

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I believe its due to the Honda fours use 1 coil for each pair of cylinders. One for 1-3, an one for 2-4. Therefore each coil fires twice per revolution. Cyl. 1 on power stroke and cyl. 3 on exhaust. Then cyl. 2 on power cyl. 4 on exhaust. To complete the firing order for one revolution, then 3-power and 1 exhaust. Finally 4-power and 2-exhaust. Wiring to the coil picks up each time it fires, witch looks like twice the revs. Wrap it around the secondary lead and your rpm's will read correct

Hibby Jr said:

I believe its due to the Honda fours use 1 coil for each pair of cylinders. One for 1-3, an one for 2-4. Therefore each coil fires twice per revolution. Cyl. 1 on power stroke and cyl. 3 on exhaust. Then cyl. 2 on power cyl. 4 on exhaust. To complete the firing order for one revolution, then 3-power and 1 exhaust. Finally 4-power and 2-exhaust. Wiring to the coil picks up each time it fires, witch looks like twice the revs. Wrap it around the secondary lead and your rpm's will read correct

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Makes sense, I'm trying to find more info some stuff I read says to add a resistor, but I can't seem to find more info. Wrapping it around the spark plug wire didn't really work, think it's to insulated to get a good reading.

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In the instructions it tells you how the set the RPM "number of engine rotations per signal".


There are 4 options - 0.5, 1, 2 and 3.

As well as the above, you can also add a 1M ohm resistor in line with the tach lead to help settle the signal.

hillsy said:

In the instructions it tells you how the set the RPM "number of engine rotations per signal".


There are 4 options - 0.5, 1, 2 and 3.

Click to expand...

I didn't see that in the instructions, I'll look again and try to find them online and download them. I'm guessing it will be one per signal. I have resistors sitting around I'll see how it looks after I figure out that setting as well as the speed setting

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