1996 Johnson 50 hp prop size help for 13 whaler

[imnotniko]

Whatsup I recently swapped my whaler 13 from a 25 hp engine to a 50 hp engine. I also added a Kent fabrication bracket to allow the whaler to run the 20” shaft 50 hp.


currently it has a 13.75 x 15 aluminum 3 blade prop. After a water test she will only run 4200 max rpm at 27 mph. The motor is a 1996 Johnson 50 hp 3 cylinder engine.


I believe the setup is over propped. Can anyone point me to a right prop to run 5500 rpm’s. I would like to hit 40-45 mph.

 

[imnotniko]

[No message]

 

[racerone]

I believe there is something wrong with your 50 HP motor.

 

[jimmbo]

Vote #2 cast for something wrong with the Motor,

 

[imnotniko]

I believe there is something wrong with your 50 HP motor.

Motor runs strong. 110 compression in all cylinders. Carbs rebuilt last season. The prop is beat up I can share a photo of it.. so I wanna replace that no matter what. My next thing is to check the timing and adjust it if need be.

 

[racerone]

I would say it is running on 2 of 3 cylinders.--Perhaps a cylinder sleeve out of position ?----Or a spark issue.-----Timing does NOT go out of adjustment on these motors.----Well except for a sheared flywheel key.------Up to you to do the trouble shooting.

 

[F_R]

Last time I ran a 13' Whaler with a 40hp motor was many years ago, and it was almost scary. Not too sure I'd want to try it at 45mph. Different strokes for different folks, I guess.

 

[oldboat1]

^^Similar memory.

 

[imnotniko]

I would say it is running on 2 of 3 cylinders.--Perhaps a cylinder sleeve out of position ?----Or a spark issue.-----Timing does NOT go out of adjustment on these motors.----Well except for a sheared flywheel key.------Up to you to do the trouble shooting.

The carbs were rebuilt last season and throttle is 100 % open. We discovered today that she’s not running on all cylinders at full throttle. I have replaced plugs/wires/coils and cleaned up the connections / grounds but have not touched the cdi. Do you have any recommendations? I have yet to water test again.

We also checked timing and it was 2 at idle. 18 full throttle (she hits full rpm’s on just idle revving)

My new prop should be here tomorrow I went with a 12 x 13 pitch.

 

[racerone]

No such thing as testing " full throttle " with motor in neutral or on a trailer.----That test means nothing.-----No surprise that it was not running on all cylinders.-----Why did you replace all the coils ??