On a similar note, my Gaffrig tach jumps around a bit (a few hundred RPM) at about 3000RPM, then settles back down as the rpms rise. It does make me wonder if I am reading high or accurate at full throtle though. I have talked to the selling marina, not very helpful (they are also no longer a Formula dealer I should add, good thing).

Gaffrig told me it may be noise in the wiring, how can I tell? I also do not have access to a second tach to verify the reading, hate to buy one just for testing this one.

Any suggestion before I purchase a new tach?

That tach should be adjustable. I have a Medallion tach in my 86 242. It was off by a few hundred RPM and I was able to adjust it. There should be a screw on the back, maybe covered by a rubber plug I can't remember. Get a digital tach, hook it up to the motor and adjust your guage to match the digital. Real easy.

If the tack is jumping Gaffrig makes a filter that may work. You can put it in line and it should be good.

Jon