Mercury XR6 fuel loss

[dingbat]

I haven't removed it... but I don't think it was there when i bought the boat. Would it be in the 90 steel elbow that screws into the top of the fuel tank? If so it is hollow. Line runs from bulb to this elbow and the elbow has a line and screen running to bottom of the gas tank

The valve typically screws into the elbow at the top of the tank. Usually doubles as the hose barb for the fuel line (hose) connection.

A leak downstream of the fuel pump will not allow the system to hold a prime. Fuel simply siphons back into the tank when the fuel pump stops. A hole in the fuel pump diaphragm will behave similarly.

A functional anti-siphon (check) valve will prevent the fuel from flowing back into the tank even if a suction side leak is present.

Make sure all connections are secured with the proper hose clamps. Hoses that are not soft and pliable should be replaced.

At a minimum, a hose should trimmed equal to the length of the hose barb to remove any hard, dried rotted material from the connection.

 

[colaynug]

Thanks gentlemen,
I got a portable tank today ... but went fishing instead of putting it on. I will get it ready and go from there
Appreciate all the input. Sounds like even if my boat came from Triton w/o the anti-siphon valve it may still be good to install one. Going to do one thing at a time and will post when I finally get it fixed.
One other thought Ive had is even though I have rebuilt the fuel pump (using OEM parts ) there maybe a hair line crack in the body casing ??

 

[Dukedog]

was gonna suggest ya re-visit tha pump but think you said you've been there twice already.. with todays gas and reliability of ALL parts, oem and aftermarket, it may take a few times ta get it right.. jus sounds like that's where tha problem is gonna be... jmo. good luck with it.

 

[Faztbullet]

Its in the carb/fuel pump area. 2 things would have to happen for fuel to drain from carbs, 1st all the floats would have to be open to open inlet needles so fuel could escape and check valve in fuel pump would have to be bad.. Chances of this very slim.

 

[colaynug]

finally got it out a couple times after installing the portable fuel tank. One trip I went with it on the back deck which is above the boats built in fuel tank. The next trip I went with it in the floor, below the boat fuel tank.
Both times it worked great.... no need to reprime the bulb between stops.
So now I know its between the bulb and the tank but where ?
I have vacuum and pressure tested every line and fitting.
There is not an anti siphon valve... it came from the factory without one .... I assume because the tank is lower than the carbs ?
Any ideas ?

 

[sam am I]

Have you tried running without the tank cap on a few times? Maybe just leave it loosey goosey....

More specifically,

Think now that the engine is most likely NOT the cause, I'd "T" off a pressure/vacuum gauge on the input side of the primer bulb.

If on the main tank feed verses the remote tank feed you have a a considerable difference in the negative pressure readings between the two sources (the tank feed being more negative), perhaps the tank isn't venting properly and a higher than normal vacuum is forming in the tank (and feed hose).

When you shut down, thinking then this abnormal vacuum is held there in a sorta static/continuous draw on the bulb's input drawing it down soft when you sit extended time.......Opening the cap would also confirm a vacuum as you'd certain hear it draw in air if the vacuum was high enough.

Or

Also I know from personal experience that some hoses can internal collapse in on themselves and restrict flow on the vacuum side of the pump (left or right of primer bulb)......This would also cause a higher(more negative) vacuum reading at the suggested "T" gauge.

 

[colaynug]

Sam,
Yes sir I have run it with the fuel cap loose / off and no help.
It does have almost new hose running to the tank but that will be the next thing I do it replace it again.
Thanks for the input