Please help - Johnson Only Goes 10 MPH

[2154Boy]

I have a 1993 pro line bay boat with 1993 120hp Johnson. The boat does good at 10mph and then when I give it more throttle it's RS the motor up and doesn't go anywhere. I've bought 3 different props and still same results and them went and had the hub replaced in one and same results. I've put new plugs,cleaned the carbs,and new fuel filter. My friends keeps saying maybe it's something in the lower unit but I'm willing to try any suggestion

 

[racerone]

Did this problem show up suddenly ?-------Motor is a new installation on the boat ?-----Height of the transom is ?-----Model # of the motor is ?

 

[boobie]

Do a cylinder drop test on it and let us know what happens.

 

[tblshur]

2154Boy i would check/drain lower unit oil look for metal if no metal in oil drop lower unit and check drive shaft splines hope this helps :welcome:

 

[boobie]

Doing a cylinder drop test will tell you if it's running on all 4 cylinders or not.

 

[F_R]

He seems to be saying it revs up but doesn't go. Like something is seriously busted or else it's ventilating. More troubleshooting is needed. Let's hope it's ventilating.

EDIT: "Friends keep saying"-----are they saying a totally worn out clutch dog? Does it grind, shake and clatter when slipping?

 

[Tim Frank]

What RPM do you read on tach?

 

[racerone]

Poster has gone ---AWOL----I believe.

 

[2154Boy]

It sounds like the rpms or motor gets higher and it won't go anywhere it basically stops but the rpms stay up until I throttle it back down. It's a 1993 120 hp Johnson on a 1993 pro line bay boat which is 18'2. I'm not too mechanically inclined on boats. The propeller guy was telling me it was probably cavitating but it's the original motor so I doubt it's sitting too high. There's no jack plate either to lower it down more

 

[2154Boy]

I'm sorry I'm new to this forum and I thought I was going to get an email when someone responded

 

[racerone]

???----You doubt it is sitting too high.-----What is the model # and how high is the transom ?

 

[oldboat1]

The plate above the prop is your point of reference. Is it about even with the bottom of the boat?