1991 Spirit 175 outboard height and propeller tuning

[Tatrd]

Hi all,

First of all, I hope everyone is staying safe and healthy and I thank anyone in advance for information on their current spirit 175 set up.

I recently purchased a 1991 spirit 175 with a 2010 Evinrude E-TEC 115hp 20" shaft using a 13-7/8" x 17pitch propeller. I am currently operating with almost a full tank of gas - 40 gallons, two batteries, and two occupants (myself and one other) and can only achieve a wide open throttle of 4900 rpm with the engine trimmed for top speed over ground. The engine is mounted directly on the transom (top bracket mounting hole).

I am hoping that others on this forum could fill me in on their current spirit 175 configurations for comparison.

I have a hunch that the low WOT RPM is an accumulation of several issues. First I think it is possible that I have a few fuel issues as the tank in the boat is original. The gas could have some water in suspension but this is hard to confirm, the boat was stored with a full tank of stabilized fuel. I have inspected the inside of the fuel hoses and they look fine. I have also replaced all of the fuel filters in the boat and on the engine. I plan to test the fuel supply and quality by running with an external tank. I also think it is possible that the engine is mounted too low (the old 20" shafts on the 1990's yamaha 2-strokes are a true 20" while the 2010 Evinrude E-TEC measures about a half inch longer). I think the last issue is that the propellor does not match the engine/boat combination however I cannot confirm this without some basis of comparison and making sure that everything else checks out.

Thank you to anyone who has information on their current spirit 175 setup.

 

[Sparkdog118]

To check the engine height, take a straight edge about 4 ft long and place it flat on the bottom of the boat down the center under the drain plug. (Sticking our next to the lower unit)With the engine in the 0deg up down position, the straight edge should be 1/2 in Bellow the plane of the cavitation plate. Each mounting hole raises the motor 3/4 inch. Rule is 1 inch height for each foot of setback.

 

[Tatrd]

Thank you Sparkdog118. These spirit 175s have a modified hull so the drain plug is set in about a foot from the transom. Do I measure the “setback” from the drain plug or from the actual transom?

 

[Sparkdog118]

Very welcome. Measure from the drain plug. Cavitation plate should be 1 1/4 to 1 1/2 inch above the plane of the straight edge.