Prop for 1988 Evinrude 175 on 20' center console

[Captain Koz]

I have a basic 1978 Aquasport 200ccp Center Console (no tee top or heavier equiptment) with a 1988 Evinrude 175. I just got the motor this season. It seems like the motor is straining and a bit bogged down in the upper rpms. twice the motor came to what seemed like a catastropic clanking stall at near full throttle only to start right back up a minute or two later. It is spordaic... I ran 30 mins straight with 4 passengers with no problem, to the next day having it stall in 1/4 of the distance, then run fine the rest of the day. Im running a 14 1/2 by 18 prop. Is this prop too aggressive leading to engine strain? I must confess that my waring alarm is broken so I dont know if it is a vacuum problem with the fuel delivery. I dont think she is overheating because I have a temp gauge and she is running between 116 and 125. New water pump. New tstats. New head gaskets. I am installing a new alarm tomorrow but i figured id throw the prop question out there to see if I can rule the prop out. I dont have a tach so I cant tell you what RPM but i can tell she is running quite labored over 1/2 throttle.Thanks

 

[hwsiii]

Re: Prop for 1988 Evinrude 175 on 20' center console

Koz, if your gear ratio is 1.86:1 I show you should be running an 18" Pitch aluminum prop at about 41 MPH with a total all up boat weight of 3,200 pounds. If you are running a stainless prop it may be too much of the wrong blade geometry. Give us the make and model of your prop please.

H

 

[Captain Koz]

Re: Prop for 1988 Evinrude 175 on 20' center console

Im not sure who makes it. the only identification it has on it is a number stamped "335646". It doesnt even have the "m" stamped on it typical of OMC. Nothing. I took the prop off to see of anything else was stamped anywere else to no avail. My marine supply says its a retired evinrude number and couldnt give me any more info. I measured the prop based on directions in a website i found using the hight differential of the diameter of the widest prop blade point times 360 divided by the angle taken up by that prop blade... i came up with an 18 even. I hooked up a new alarm today and rigged a makeshift tach ( i do not want a tach on the boat) and I will run her tomorrow. I am suspecting either too much prop or upper rpm fuel delivery. I just want to try to rule out the prop through good people like yourself on this site. thanks for your help! Any more help would be appreciated.