79 25 Johnson hydrolocking

[Harry B.]

Back to my 1979 25 hp Johnson.
float is all screwed up and I can’t get it to keep from flooding the engine. It even goes to the point of hydro locking the motor (can’t pull the recoil starter) Pull the plugs and give it a pull and gas blows out big time.
Anyone heard of this??? I find it pretty crazy and haven’t had this issue.
Ive attempted to adjust the float but no joy so far. Needle valve looks good. With the needle valve in the brass fitting I can’t pass air through it either. Any advise is greatly appreciated.

 

[Scott Danforth]

first step is to replace the float and needle/seat. set the float height correctly

 

[Chinewalker]

Are you sue it's the float and needle and not he fuel pump? Float and needle would also be dumping fuel out the float into the pan. A pinhole in the fuel pump diaphragm would put fuel directly into the crankcase and cylinder.

 

[racerone]

Check the fuel pump !

 

[F_R]

And...Check the carburetor bowl vent.

 

[Harry B.]

Thanks for the replies guys!!!
I had no idea that if there was a hole in the diaphragm of the fuel pump that it would do such a thing.
I thought if the diaphragm was worn or had a pin hole that's when you had to become the fuel pump and had to keep pumping the bulb to keep the motor running for very long.
It must be bigger than a pinhole too as when I pump the bulb, it must go directly from the bulb and into the cylinder and crankcase drop for drop of gas. When I pull the recoil starter, many ounces of fuel comes shooting out.

 

[racerone]

You have to check it.

 

[Harry B.]

Thanks again. I'll pull it tonight and inspect it. Thank heavens it's not the little square OMC pump ;-)

Where would I find the carb bowl vent? Is it the the vent hole in the bowl not occupied by a screw? If so, what's the proceedure to assure it's functioning properly?

 

[F_R]

Thanks again. I'll pull it tonight and inspect it. Thank heavens it's not the little square OMC pump ;-)

Where would I find the carb bowl vent? Is it the the vent hole in the bowl not occupied by a screw? If so, what's the proceedure to assure it's functioning properly?

I was afraid you'd ask that. I THINK it comes out the front of the carb beside the big air intake hole. Sorry, I don't have a carb to look at. What happens is if the vent is plugged, air will collect in a big bubble above the incoming fuel. The bubble prevents the fuel from rising, thus it doesn't raise the float to shut off the incoming fuel. So the fuel keeps coming in and goes up through the main nozzle.

Your motor has a silencer, so this might just be a bad guess. Mud wasps love to stop up the vent hole in motors without a silencer covering it.

 

[fireman57]

If your tank is sitting in the sun and not vented it will build up pressure and force fuel through the carb into the cranckcase.

 

[jimmbo]

Make sure the float is not installed upside down. It has happened.

 

[Harry B.]

It was more than a pinhole. Two quarter inch tears in the diaphragm. Hopefully this solves the extreme flooding issue.

 

[racerone]

I would say that will solve the issue of one cylinder getting way to much fuel.