25hp Johnson surging at WOT

[c-dubb]

I recently purchased a 25hp Johnson J25ELCTD that the previous owner said shut off on him the last time he took it out. I cleaned the carb and installed new needle, seat, float, and gaskets. I found the top coil oozing a sticky substance and replaced it as well. The engine will crank and idle fine, but will not always run WOT without surging. When it does this, i can pull back to about 3/4 throttle and will do fine. Looking for some advise on where to start looking next. I have verified the vent on the fuel tank is open. Thanks in advance for any help.

 

[James R]

That symptom is typical of running low on fuel in the carb. Try squeezing the primer bulb when the motor surges. Could be the pump is sucking air. Could be the pick up tube in the tank is partially blocked. If it is the fuel pump the primer bulb test will show it.

 

[c-dubb]

I wont be able to try anything until this weekend. I am thinking about trying a different tank and primer bulb also since I have access to them. I will also have a passenger who can prime the bulb when this happens again. I will post my findings then. Thanks again for the input.

 

[flyingscott]

A low float level can cause that to. The bowl is a reservoir that needs to hold enough fuel while the float is cycling. How did you set the float level.

 

[c-dubb]

I set the float to be level with the carb body at the time that the needle valve closes.

 

[c-dubb]

I replaced the fuel lines, bubble, and tried a different fuel tank. I also adjusted float to allow a little more fuel into the bowl. I think we may have solved it, but I didn't test too long because my lower unit started separating from the motor. It appears that the previous owner hit something and sheared a bolt or two that wouldn't hold up to running WOT. I will post my results as soon as I get back in the water.

 

[jakedaawg]

Surging may also be obtained by a bad prop hub especially if it came to a "dynamic halt" at some point. (I sure like that description, i think racer used it first though)

 

[c-dubb]

Got lower unit put back together this weekend and it ran great. Not sure exactly which thing was responsible, but i will test the tank out later on with fresh fuel just to have a spare. Thanks for all the help guys.

 

[Joel45]

Hi all first time post, and sorry for resurrecting an old thread but I have the same symptoms on my motor.

I have a 2000 model that is surging at wot. I have rebuilt the Carby and checked the float level twice now. I am running a direct brand new fuel line to the fuel pump which is also brand new. The surging stops when I pump the primer bulb and runs like a dream. Just seems to be starving for fuel at wot?

Could the carb be running to rich? I just cant seem to work it out. Any help would be much appreciated

Cheers