1965 Vintage Johnson outboards

[EZ]

I had asked in my last message about increaseing the h.p. on my 16hp motor, I know that Johnson made 18,20,and 25hp motors that year, what was the basic difference, from the outside they all look the same and if the bore and stroke is the same on these engines then it must be caburetor,RPM,or timing that increased the HP EZ

 

[JB]

Re: 1965 Vintage Johnson outboards

Howdy EZ.<br /><br />This is a second thread on the same question. Not a good idea.<br /><br />It should be an addition (reply) to your original thread.<br /><br />Good luck.

 

[Chinewalker]

Re: 1965 Vintage Johnson outboards

Hi EZ,<br /> In 1965, Johnson only made the 18hp in that range. The larger variations on the 22 cube didn't come out until later in the 1960s when they did a major redesign of the motor, adding heftier rods and crankshaft, 2-ring pistons and larger carburetor to get the horsepower boost - and keep the motor together in the process. Bosting your existing 18hp to 20 or 25 would be much easier if you simply found a later (1968, I think, or onwards) 20/25 powerhead. Your second best bet would be to ensure you're getting all 18hp as it is - running ring-free in your gas, spraying some Sea Foam down the throat and cleaning up the innards, and making sure you're spinning the recommended revs (4000-5000 operating range with 18hp being rated at 4500 revs). Is your prop the proper one for your load? Is it clean and free of burrs and dings? Lots of stuff you can do within your existing motor to get a little more kick....<br />- Scott

 

[EZ]

Re: 1965 Vintage Johnson outboards

Thank you Scott this is the info. I was looking for, people have been telling me to just change the main jet and run the engine faster, having been in the mechanical field for 50+ years that sounds to good to be true,and the way it looks that is the case. EZ