70HP to 90HP Tach Conversion

I have re-powered from a 2000, 70 HP to a new 2007, 90 HP. Both 2 strokes. I first had an issue with the trim angle plugs on the harness but I got that figured out. Today I went for the first break-in cruise and noticed that the tach appears to be reading twice the RPM that the motor is actually turning. The tach is a 2000 vintage multi function tach/oil level/trim angle. There must be a difference with the pick-up coil(s) or something. Is there anyone that has information to fix this.

Giving a double RPM reading is typically what happens when you run a 2-stroke on an instrument that thinks you have a 4-stroke engine.
Is your instrument the 6Y5-8350T-81-00? If so, check your DIP switch settings at the back of the instrument, behind the little rubber plug/grommet.

I bought the boat used and can't see any markings on the tach itself. I'll have a closer look. It worked fine with the original 2000 70 HP 2stroke?

Thanks

[boats.net]

Change the setting on middle dip switch to the down position for 12 pole alternator. The three switches should be up, down, down.