Tach 2k RPMS off---reading inaccurately.

[eventer289]

I am posting on behalf of my father. We recently purchased a 1987 Z33. It finally got put in the water today and the right engine is reading about 2k rpm off from the left. I know that this cannot be so, because when going about 30-35 mph the left engine reads 2800-3000 rpm while the right reads that it is at 5k, even though I can tell they are both turning about the same rpm. What would be causing this and how can it be fixed?

[MOP]

Look at the back of the tach there is a compensating screw, it is usually marked 4-6-8. Even if it is on the correct marking try turning it back and forth a few times, the contacts can get crusty. This may or may not be the problem but is common.

Phil

[Formula Jr]

unless you are looking at something different Phil, its not really a screw, more of a slotted selector switch to select the right resistor for 4, 6 or 8.

[zelatore]

I've seen this on a lot on older tachs. Usually I find it's just bad connections, although sometimes I end up replacing the tach.

I'd try cleaning the connections both at the tach and the engine - it's free and easy, so you've got nothing to loose.

It's possible the tach is set wrong, but I wound't expect it ... why would somebody mess with it after all these years? But again, it's easy enough to check and doesn't cost anything.

At least for most of the tachs I deal with, they aren't very expensive. When one of the tachs on my own Carver started acting up, I just replaced both of them with new Teleflex units. The orriginal design wasn't available but these are so close nobody has ever commented that the tachs are different than the other gauges. Now if you're running Livorsi or something it's a different story - $$$

[maddad]

Or like the back of my SW tach, there are 4 small switches under a cover and the right pattern needs to be selected for the right number of cylinders.