Mercury 150 Fuel Mileage - 1971 20' SF

[McGillicuddy]

Yea, I believe your XRi is a 2.5L as well. Maybe Bigshrimpin will confirm or correct that. If you have gps just run it off a 6 gallon tank and measure your distance for a gallon every 500 rpms from 3000 to 5800 rpms. Then do the math.

First you'll have to change your prop as you appear to be over-propped.

Pitch is only one factor in getting the right prop. What brand, model, and diameter is the prop? Al or stainless? Ask a boat/prop shop or friend to loan you a used aluminum 15 x 17 black max or black diamond Quicksilver # is1912 2X. I am certain you will see improvement in every performance category. That should get you closer to your target rpms and make your motor happier. And contrary to popular belief, you will likely see economy increase with less pitch. and the right prop. perhaps I overestimate that motor but I think you should see mid 40s at 5800 rpm on a 20 with that motor and the right prop.