Tachometer accuracy


I recently had some problems with my tach. Thought I was topping out at 3800-4000RPM but after re wrapping the wire I am getting 7-8000RPM readings. That tach would turn off and reset all the time so I took it off and replaced it with a different unit. On the original unit I wrapped it around the plug wire 5 times like was recommended.

New unit is reading closer to the high readings of the old one but it raises the question:
The wraps apparently influence the readings, so how to know what is accurate and how many wraps?
Obviously the bike wasn’t topping out at 3900RPM, but is it really turning 8000RPM?

I have some TAV parts coming so I want to get those in first, but supposed to engage at 2800 but now engages at 3800-4000
Do I use the engagement of the TAV to set the tach?

Thanks for any advice
You probably have the tach set to the wrong type of engine. Depending on the setting, my tach can read double the actual rpms.

As far as accuracy, mine only changes about 100-200 rpms depending on 4-6 wraps of the wire. Compare your rpms to your gps speed, gearing and tire size and you can get the tach to come pretty close to your true rpms, +/- 100.
If there is no way your engine can spin 8000 then the tach is either broken, installed incorrectly or the setting is incorrect. just change the setting until its close to your calculated rpm/MPH. It appears you may be doubling your rpms so its gotta be the setting. I could be wrong but pretty sure four strokes are 2 sparks per revolution. Either way, just change the setting and it should work.
Motor is modified so it could be turning 8000
Thanks I will try some different settings and see what that does.

Well I was thinking that each time the crank turns one revolution, it sparks once.