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Tach Oddity

560 Views 1 Reply 2 Participants Last post by  TCIII
Trying to teach my grandkids how to shift gears, I decided to put a tach on my LT-4WD-250. Simple install, just wrap the pickup wire around the spark plug wire 4-5 times. I used velcro to stick it to the dash just under the speedometer.

This is a generic tach that also has hour meter on it, which, oddly enough, it had 20 hours on it.

It has several settings for various types of motors. The setting I thought it should be in the 1P2R, which is simply 1 spark per 2 revolutions. When I tried that, it read that the RPMs were around 2x (1800 RPM at idle) what they should be.
So I decided to try 1P1R, 1 spark per revolution. Meaning the 4 stroke would spark every time it would get to TDC. (wasted spark on exhaust stroke). But that read 4x (3600 RPM at idle) .

Finally, I selected 2P1R, which is suppose to be 2 sparks per revolution, (4 stroke-4 cylinder or 2 stroke-2 cylinder setting.) and it read about what I would expect idle to be, right around 800-900 RPM. Took it for a run and the "comfortable" shifting was always between 2500-3000 RPM. The gauge might be a bit off as I really don't have another way to check, but at least this gives me a good learning tool.

I just thought it was odd that it seems to be reading like that.
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I had the same problem. I realized the way the spark sensor on the flywheel works, it fires on every rotation....hence the need to set it up as a 2 stroke.
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