140hp Evinrude 23.5ft tri-toon need prop advice

[Faztbullet]

If needle tach doesn´t return to 0 when engine is turned OFF the tach has issues

I doubt theres anything wrong with tach as they stop at the engine RPM when shut off. It should only read zero when key is turned on. You have the big gear case and the 17 is about right for just cruising....

 

[ahicks]

Your original note indicates you have a 13 spline shaft. It looks like the new prop you have is a 15 spline?