1958 johnson 18hp

[Math.?.]

Hi, I have a 1958 johnson outboard motor and i am not sure it is giving it´s full power. Is their a way to know if an outboard is giving its full power? Thanks.

 

[1946Zephyr]

I would do a spark test on it. You can also pull the hand starter assembly off and remove the inspection plate on top of the flywheel. Once you remove that plate, you can turn the flywheel by hand (clockwise only) and see your coils. If you see cracks, then your coils are shot. It's likely, that you're running on one cylinder

 

[OptsyEagle]

You could put a tachometer on it. These motors were rated for 4500 rpm. If you are getting that you are getting all she's got.

If you suspect that you are seriously low on power, it would probably be from a failed cylinder. These things run almost undetectable on one cylinder with the only exception being a lack of top end power. To do the test, just start it up and let it warm up for a couple minutes. Put it on a fast idle and with a set of insulated pliers pull one spark plug boot at a time. If the motor stays running both are good, if it dies when you pull a boot you know the other cylinder was never firing or is very weak.

 

[64osby]

May want to give it a compression test. I installed a new head gasket and milled the block and head on my 57 18 hp. Compression went from 60 to over 100. Runs very strong now.