1987 Johnson 175HP - Bogging at Hi-Speed

[Gotts]

I purchased a used 175HP 1987 Johnson 2 years old and by enlarge the motor runs well, however every now and then when I running at full throttle the motor starts to hesitate and loose power. I find if I throttle back it stops the hesitation, but when I throttle back up it starts to hesitate again. It feels like it's cutting out or losing a cylinder or two. No alarms
As well, Does anyone know the estimated top speed of this motor. It's sitting on a 19 foot Kona skiboat.

Thanks Fellas.

 

[ezeke]

Re: 1987 Johnson 175HP - Bogging at Hi-Speed

After testing compression, the first thing to check is the fuel supply to be sure that the float bowls are staying full during sustained high speed running.

Start at the tank and work your way to the carburetors.

If you have a inductive timing light, you can use it while running to be sure that your spark is good through the top end.

The theoretical maximum top speed depends on the propeller pitch.

 

[Gotts]

Re: 1987 Johnson 175HP - Bogging at Hi-Speed

Thanks Ezeke, I apprecaite your thoughts. I'll run through the whole system as you suggest.

I'm using a 19 X 14 1/2 pitch stainless prop.

Thanks again

 

[ezeke]

Re: 1987 Johnson 175HP - Bogging at Hi-Speed

If your gear ratio is .538, a 19 pitch prop at 5500 engine RPM would give a maximum theoretical speed of about 53 MPH.

(19" X 5500 X .538)/12 = 4685.083' per minute.

(4,685.083' X 60)/5280 = 53.24 MPH