1960 18hp Evinrude Fastwin NEEDS More Power

I just got an 18hp Fastwin and took it out on the water for the first time last weekend. It is on a 14ft bluestar runabout with Johnson throttle controls. The boat motor fires right up on the 1st or 2nd pull but seemed under powered. I did realize that I was running 50:1 instead of the proper 24:1 mix. Could this be the main problem? I was going to replace the spark plugs this week and I am wondering what else I should do to try and tune it up a bit.

Looking for advice!
Thanks!

I think a general tune-up would work wonders. Specifically, check the coils and points and clean the carb.

Helps to know what year engine we are talking about and what kind of performance you are currently obtaining.
You may have damaged the engine running half of the recommended oil necessary for that engine.

1960 and it starts fine, runs smooth but just feels very under powered. It feels like an 8 or 10 hp it does not feel like an 18.

I am going to borrow a kit and do a compression test on this weekend, how do I know what the compression should be on the moto

I don't know what the specs are for your motor, but if you get around 130psi and each cyl is within 15psi of each other you can probably assume that is good.

Check to see that the carb is going to WOT, there should be a roll pin at the end of the butterfly shaft that you can see go to vertical to verify.
I can see the low speed adjustment at the front of the engine. That was around the time the high speed became a fixed jet. Does yours have a high speed needle or a fixed jet? If it has a needle then lightly seat it and go out to around 1 turn. Accelerate and slowly close that needle until your highest RPM is obtained then open the needle just a touch for a little insurance. These are easy checks so please do these and let us know.

It has a low speed and high speed needle. I am going out to the lake this afternoon, I will run these checks along with the compression test and let you know. Thanks

Ok, didn't have much time to play with the motor tonight but I figured out a few things. The compression is 92 in both cylinders, is this good or low?? I think part of the issue is the throttle control cable and throttle handle, I think the housing is limiting the handles motion and not allowing it to go full throttle, I will be taking this apart and checking it in detail on Sunday. I have been reading about this carb cleaning method of using seafoam in the mix along with spraying it into the cylinders after removing the plugs. Have you tried this, does it work? Is it worth the effort? It does sounds a lot cleaner with new plugs and the proper gas oil mix...

I wouldn't put SeaFoam in the cylinders, It'll wash the lubrication off the Piston Rings. SeaFoam is a fuel system additive and a Good One, I use it in everything. The 50/1 oils will lubricate that old motor just fine and not foul any spark plugs in the process. Is the shaft length correct for your boat? How much weight are you pushing with it? Remember it's 43 years old.
Good Boating! 8)

Had it in the water last weekend and figured out the issue, it was a warn rubber stopper that is part of the throttle, it was warn down so it wouldn't let the throttle open up all the way. A few adjustments and everything was running great! Thanks for the help guys.