Excessive fuel pressure

[jerseyjimk]

I have a 2004 Yamaha 4 stroke 60/40 jet outboard, for the second time the number 4 cylinder was filled with gas, to the point where it wouldn’t turn over. The gas can portable has a vent cap, always left open, check twice. I can’t figure out why all the fuel pressure. How bad is that, with the cylinder filled, I take the plug out and drain, then start the motor. Starts right up, any ideas????. This ones got me, check the vent cap, its clear.

[99yam40]

Not sure if the #4 can fill up from a bad fuel pump or not, but something to check on

[jerseyjimk]

Motors not running, so I don’t think it’s the pump,it fills when sitting in the yard. This is the first time I’m having this problem. Nothings changed except for the fuel separator.

[99yam40]

Fairly sure it is a fuel injected motor so either the injector for #4 is dumping fuel or pump could be leaking.
how else could fuel get into a piston chamber

[TownsendsFJR1300]

The engine is a "normal" OB configuration correct(just a jet drive lower unit)?

With the #4 cylinder being the lowest cylinder sounds (as noted above), like fuel leaking into the cylinder.

As we don't have the MODEL # for the machine, a carb needle leaking, bad float-leaking, would allow fuel into the cylinder.

If fuel injected, a stuck open injector would allow the entire fuel rail to empty (gravity)to the #4 cylinder.

A little more info on the model, if FI'ed, carbureted, etc would help..



This 2004, 60 HP, 4 stroke is carbureted: https://www.boats.net/catalog/yamaha...jrc/carburetor

[jerseyjimk]

Its a carburetor motor, yes its a 60/40 jet, the power head is 60hp. Would it be just the #4 cylinder carb or anyone of them for flooding the # 4 cylinder

[TownsendsFJR1300]

Its a carburetor motor, yes its a 60/40 jet, the power head is 60hp. Would it be just the #4 cylinder carb or anyone of them for flooding the # 4 cylinder

Each carb goes to each cylinder so it would have likely have to be the #4 carb. IDK if there's any hoses for the choke but likely not.

You may try disconnecting the fuel line to the #4 carb for a day or two and see if you get a "full cylinder" (just to confirm)

About the only way for the carb to fill the cylinder is if the needle and /or needle seat inside the carb is leaking or float is leaking staying open.

You can inspect / clean #4 carb, test the sealing of the needle/seat with a vacuum gauge hooked to the inlet of the carb while it's held upside down. It SHOULD hold A VACUUM when closed..

[99yam40]

just to clarify the last post more, each carb feeds only it's own single cylinder

[jerseyjimk]

That is correct, 4 cylinder, 4 carb motor

[jerseyjimk]

Each carb goes to each cylinder so it would have likely have to be the #4 carb. IDK if there's any hoses for the choke but likely not.

You may try disconnecting the fuel line to the #4 carb for a day or two and see if you get a "full cylinder" (just to confirm)

About the only way for the carb to fill the cylinder is if the needle and /or needle seat inside the carb is leaking or float is leaking staying open.

You can inspect / clean #4 carb, test the sealing of the needle/seat with a vacuum gauge hooked to the inlet of the carb while it's held upside down. It SHOULD hold A VACUUM when closed..

Thank you, I will try that.

[walleye1]

Thought it was fuel injected?

[TownsendsFJR1300]

Thought it was fuel injected?

Not per post #6..

[99yam40]

I thought it was an injected motor because it was a 4 stroke.
I was wrong

[jerseyjimk]

I took a look at the carbs, unbelievable,looks like I have to remove the whole intake to get to the #4 carb. I hope this solves my probelm, I will let everyone know when i get the job done

[jerseyjimk]

Could this carb problem set off my buzzer???Thats another issue I’m having at idle, only!!