1973 25hp Johnson only reaching 5mhp

[BrandonGunther]

You
I've got a 1973 Johnson 25hp outboard motor. Runs great in all aspects and in the barrel test putting it in gear it audibly sounds and visually seems to reach full throttle and max rpm but after putting it in the river it doesn't sound like it's reaching max rpm and only pushes about 5mph. Also appears to have gas in line coming out of crank case. Any ideas?

 

[F_R]

Motor is running on one cylinder. Begin with a compression test to make sure something inside isn't broken. Then check ignition system. No, it ain't the carburetor.

 

[Crosbyman]

prop hub spun ? drive pin etc...

 

[BrandonGunther]

Motor is running on one cylinder. Begin with a compression test to make sure something inside isn't broken. Then check ignition system. No, it ain't the carburetor.

Compression is 145 in both cylinders. Starts right up and stays running. I don't think ignition system is having any issues

 

[BrandonGunther]

prop hub spun ? drive pin etc...

When it's running it doesn't change audibly. I'd think if it was a prop hub or drive pin it would either Rev high or bogg wouldn't it?

 

[Crosbyman]

whatis left ? throttle likage ?

 

[racerone]

There is an oil recirculation line on this motor.-----But replace the fuel pump diaphragm and test again.

 

[F_R]

Compression is 145 in both cylinders. Starts right up and stays running. I don't think ignition system is having any issues

Phooey. They will start and idle great on one cylinder.

 

[racerone]

F R----Why do folks make all these assumptions instead of some simple testing??-----But then again that has not changed for 55 years or more.

 

[BrandonGunther]

Phooey. They will start and idle great on one cylinder.

I replaced both plugs. I will say day one it was running on one cylinder. I could hear it and I had a fowled plug. However since putting new ones in its not making that noise. But I'm still not getting speed.

 

[BrandonGunther]

There is an oil recirculation line on this motor.-----But replace the fuel pump diaphragm and test again.

I'll give it a try.

 

[F_R]

Speaking of assumptions, we always assume it is the motor. Never the boat. Got marine growth on the bottom? Carrying around 400 pounds of water under the floor?

 

[BrandonGunther]

Speaking of assumptions, we always assume it is the motor. Never the boat. Got marine growth on the bottom? Carrying around 400 pounds of water under the floor?

It's on a 15ft 1975 Meyers fishing boat. No marine growth however there could be 400lbs of water soaked into the foam. Do you think it would effect it that much?

 

[racerone]

Start motor.----Pull one plug wire off at a time.----Report what you find.

 

[BrandonGunther]

Start motor.----Pull one plug wire off at a time.----Report what you find.

Off the spark plugs?

 

[racerone]

Correct ---off the sparkplug.

 

[airshot]

To get accurate results and recomendations we need positive test results, not "I think or sounds like"... these are not accurate nor will recomendations be accurate. You need to do some positive, accurate testing to know for sure, other wise everyone is guessing and that gets you nowhere.