Evinrude 50 faster than johnson 48

I have a 20ft pontoon boat with a 1992 Johnson 48 that does around 12mph. I pulled off a 1983 johnson 50 due to lower unit problems. My 1983 pushed my pontoon boat @ 21mph. Johnson 48 runs awesome but is just slow. I am just wondering why my old evinrude 50 is twice as strong? Is it geared different? I pulled the prop off of the 50 and installed on 48 so i know that is not the problem.

Re: Evinrude 50 faster than johnson 48

The Johnny is sick. A '92 48SPL is actually a more powerful engine than a '83 50 because of the prop rating vs powerhead rating.

You need to go to the JohnnyRude Troubles forum and get some help with troubleshooting.

johnson 48 slower than evinrude 50?

johnson 48 slower than evinrude 50?

I recently replaced my 1983 evinrude 50 with a 1992 johnson 48 due to lower unit problems. My evinrude 50 pushed my 20ft pontoon @21 mph. My 48 pushes it at 12 mph. I was wondering if the 1983 evinrude 50 is that much more powerful than the newer johnson 48? Johnson 48 is running with the prop that was pulled from the 50. The 48 has clean carbs and starts and runs awesome other than being slow.

Re: johnson 48 slower than evinrude 50?

Re: johnson 48 slower than evinrude 50?

What RPM's are you making at 12 MPH, and what was the 50 making at 21?

Possible a higher gear ratio makes some of that difference.
Did you make sure the throttles are horizontal (and not beyond) at WOT, and the spark is advancing fully?

Any chance the new motor is a longer shaft than the old?

Trimmed the same?

Re: johnson 48 slower than evinrude 50?

Re: johnson 48 slower than evinrude 50?

something is not right.

Re: johnson 48 slower than evinrude 50?

Re: johnson 48 slower than evinrude 50?

My first thought is did you put the correct prop on the the 48.
Sometimes to the untrained eye a motor running on one cylinder will seem fine except for a lack of power.And you are at almost exactly 1/2 speed.

Re: Evinrude 50 faster than johnson 48

I never tried the prop that came on the 48. I used the 50 prop on it because it was in a little better shape. Not sure of the rpms. I pulled the plug wires while running and it doesnt die on either plug.

Re: Evinrude 50 faster than johnson 48

If your using the prop from the 50 then performance should be basically the same.Check compression,check timing advance,throttle opening all the way.
you might try a touch of choke to see if its lean.

Re: Evinrude 50 faster than johnson 48

I smell a dirty carb, just for grins take an eye dropper or something you can squirt a small amount of gas into each carb whike it is running so e throttle and see if it doesn't run better for a second, you will have to pull the intake cover to get access to the throat, if not that will rule out the carbs as a cause.
I had a similar problem last year, pulled plug wires, replaced all kinds of parts turned out to be a dirty carb, and I had "cleaned" them twice, just not right.
It idled perfect and you couldn't hear a miss but it was running in one cylinder the whole time.
After spending $100+ on parts it turned out to be the high speed jet in the bottom carb

Pay special attention to the high speed jets, pull the drain plugs on the float bowls they are inside the drain holes and you will need a really skinny screw driver to take them out, run a stranded copper wire through them a couple times and there you go.
Always check the free stuff first.
My 2 cents