...

 

Could be an issue with wiring or with the distributor. The tach signal comes from the distributor, and a bouncing tach is a sign of a bad coil (I think).

 

if the needle is stable and not shuttering or moving around slightly it could be that the needle was removed and reinserted incorrectly.
Could also be the ignitor or tach itself is bad

Also, make sure the screws are tight in the rear of the cluster, I've seen a loose screw mess with the tach reading.

If you're confident about the distributor, wiring and everything else in the system, you can try to "re-cal" the tach, remove the clear cover to the cluster and plug it back in to the car.
Start the car and let the car idle till you're sure that it's at operational temp and running at 800RPM (external tach or datalogging)
Pull straight back and semi-gently to pull off the needle, then reinsert it pointing halfway between the 1k and next lower mark.
Be VERY careful not to tilt the needle, damage can be done very easily.

this is a very crude way of doing it but it works reasonably well.

 

read this: http://honda-eg6.blogspot.com/2010/1...on-how-to.html

 

Just put in an aftermarket tach like an autometer or something good