1976 25HP Johnson "waving" power loss on HIGH speed?

[andreipou]

Hello,
I have new problem with one of my 1976 25HP Johnsons (25R76E):

When running the boat it runs fine on low and medium speed, but when switch to high speed it runs fine for about 15-30 sec then the power dropps to slow and then goes back to high and again to slow and again to high, etc, etc...
It feels like "waves" of power. I do not know how else to discribe it.
If I go to medium or low it runs fine but going back to high it is the same problem.

I rebuilt this one last winter. New pointers, rebuid carb, new fuel membrane, spark is good, compression is good.
The prop I put from the same model but with different "step", but one of the specified for this model.

The tank and fuel line work fine with other motor of this model (I have 3 of them).


Any ideas?

Thanks.

 

[Cofe]

Re: 1976 25HP Johnson "waving" power loss on HIGH speed?

Sounds like a air in leakage on your fuel system. Look for pinched hoses, rubbed thin on the bottom hoses, and loose fuel line connections.
You could also try the GUM diagnosis. It goes like this, chew a bunch of gum, and put it on suspected air in leakage places, like the adjustment screws on the carb or fittings. "Silly putty works also" Hope this helps.

 

[andreipou]

Re: 1976 25HP Johnson "waving" power loss on HIGH speed?

In this case it would affect the other motor too, right?

The only hoses inside the motor are from carb to pump and from fuel inlet to carb.

 

[AlTn]

Re: 1976 25HP Johnson "waving" power loss on HIGH speed?

when the motor is "erratic" at high speed, pump the fuel line bulb...if this "cures" it...you need to address the fuel pump or fuel delivery hoses and connections..if no change..main jet cleaning,float level check, and air leaks are possible culprits