I just bought a 1975 A185F with an IO-520.

My tach is showing redline at 2,750 and a little yellow after that.

Shouldn’t the redline be 2,850? The governor is adjusted to match the tach.

What propeller do you have? Some propellers have an RPM limitation

McCauley 401 86”

I haven't looked at the STC for that prop on the 185 for a long time but I believe you're right, that should be 2850 rpm limited to 5 minutes. Hopefully someone with a better memory or the actual STC can confirm that. Of course the you should have a copy of the STC somewhere in the permanent aircraft record as well as a flight manual supplement.

probably not original or even from same model. I have a 75 and it looks different but it is not the original either. The MT is the only current RPM limited one I know but good luck finding a straight answer on what it is.