1975 50 HP Johnson Outboard

I have a 1975 50 hp Johnson outboard motor. When I put the muff on it out of the water and tune it it idles good and does not die. When I take to lake and put in the water it does not won't to stay running and dies. It seem the back pressure has and effect on the motor and the way it runs. can you help please.

Thanks, Craig

Re: 1975 50 HP Johnson Outboard

yup, oldest story in the world. lack of backpressure enables the motor to run fine on land, then crap out soon as you put a load on it.

add about 150 to the idle speed when you're setting it at home then fine tune it on the water.

Re: 1975 50 HP Johnson Outboard

As jtex said above, almost anything will run fine with no load. Had the same problem on my 15hp rude, mine just happened to be a coil that would heat up and fail. On one cyl she ran like a champ on muffs, was garbage on the water. Start with the basics though, make sure you have good compression, then fuel, then spark.

Re: 1975 50 HP Johnson Outboard

Do I need to screw out the fast idle screws another 1-1/2 turn besides the 1-3/4 turn ?

I think it just the carbs not set right because when i am able to keep it running long enough to get in gear it does fine and it plains out well. I think it just needs a fine tune job.

Thanks, Craig

Re: 1975 50 HP Johnson Outboard

Just to be sure (sometimes there's confusion on this point), there's the idle mixture screws on the carbs to adjust the fuel/air mix, and there's also an idle set screw (don't know exactly where on that particular motor, but your manual will point it out to you), to raise or lower the idle RPMs.

Click on the "top secret file" at the top of this forum and follow the link to the joe reeves thread on setting idle mixture screws. Follow that procedure then set the idle speed to your target (whatever your manual says it should be in gear with the boat in the water) plus 150 or so. All that on the muffs.

After you get the boat in the water, readjust the idle set screw if needed to get the idle RPMs where they need to be. You might decide the mixture screws need readjusting, but they ought to be ok.