Strange behavior

[Hoppetossa]

I have a mercury 5hp 2 stroke from 2000.
It needs more gas then normal to keep it running (the idle screw is not sufficient enough). The carburator is cleaned. The strange thing is that when I take the fuel line off (external tank) it runs like it should till the carb is empty. I checked the close off needle and it closes of the petrol when I keep the carb upside down. When I connect the fuel line the strange behavior returns.
What can this be?? I worn out needle (but it closes off).

 

[QBhoy]

Either the fuel line and primer bulb from the remote tank is the wrong way (they only go one direction), or you remote tank has the vent closed…or the remote tank has crap fuel

 

[Hoppetossa]

I am afraid non of these things. Everything checked, new fuel etc. I am thinking of the direction of a worn fuel stop needle (or however it is called).

 

[flyingscott]

What happens if you pump the primer ball? Does it keep running.

 

[Hoppetossa]

It doesn't so I think the needle is worn.

 

[racerone]

Fuel pump diaphragm has a hole in it ???

 

[Hoppetossa]

No, the fuel pump is in good shape.

 

[Scott Danforth]

compression numbers?

interior liner of the hose has deteriorated and is clogging the fuel line, or the line has a hole in it

a worn needle would not do it because that is basically an on/off type of device to limit in-coming fuel. a sticking needle, maybe

 

[Chris1956]

Sounds like the carb is partially flooding. I would replace float and inlet needle and seat. Those are maintenance items anyway.

BTW- it is not unusual for an OB to run real well when the fuel line is disconnected. They like that lean mix at idle, however, it would be too lean to allow acceleration, as carbs do not usually have a accelerator pump.

 

[Hoppetossa]

Sounds like the carb is partially flooding. I would replace float and inlet needle and seat. Those are maintenance items anyway.

BTW- it is not unusual for an OB to run real well when the fuel line is disconnected. They like that lean mix at idle, however, it would be too lean to allow acceleration, as carbs do not usually have a accelerator pump.

I hope I can go to a service dealer Monday. I am in Greece so things are not easy to get. I hope he has the parts to renovate the carb. I hoped bending the needle holder a bit could help but it didn't. The carb only contains les petrol. The story continues Monday. It also explains why the engine was starting easy in the morning, the carb was empty and I filled it up a little. One pul and running, after that I kept pulling with 3/4 gas to get it running (which it did).