Fuel tank venting

R

rockyrr

Member
Joined
May 5, 2007
RO Number
26166
Messages
29
We have a 21' walk-around with a Yamaha 150 4 stroke. We may have a block vent, so we're told (from another post). My problem is that I don't know where the vent begins and ends; and, if I do locate it, how do I go about unclogging it? I sure could use some guidance on this issue. Feedback appreciated.

Thanks
 
One place to start is to find the exit of the vent.

Typically, this will be a "clamshell" fitting located on the side of the hull, above the waterline ( sometimes on the transom ).

Some vents have a screen protecting the opening. Visually inspect the screen to see if corroded or blocked by a mud dawber wasp nest ( both common )

You should also locate the tank end. There are typically only four things that will exit your fuel tank: Large diameter fill tube, smallish diameter fuel line to engine, "medium" diameter vent line, and the fuel level sensor ( wires attached ).

Be sure not to allow a spark or flame anywhere near as you inspect and or fiddle with the line!

If vent fitting screen on hull is corroded, replace. If wasp nest, use something that will not cause a spark to remove mud. Any other cause ( kink in line, water/fuel resting in sag in line, foreign object in line must be removed via other methods, incl possible replacing line.
 
If your fill cap is in a spot where it won't get spray if you test run without it on a very smooth day, trying that bypasses the vent to indicate whether vent is clogged or not. Sometimes a shot or 2 of PBBlaster on the vent screen will unclog a corroded vent , and used a couple times a season will prevent corrosion issues.

But if you don't see the tank fill vent fitting on the upper side of the hull or transom, you might instead have a vented deck-fill fitting.

If you fully fill the tank , you may have a slight "spit" of excess fuel out the vent wherever yours is located.
 
If you can manage a 2-lb to maybe 5-lb air pressure at the Filler cap, and see if the pressure falls off immediately.
If it does, the Relieve tube is OK.
If it doesn't, that Relieve tube is blocked.
Finding it shouldn't be too difficult. It will be outside the Cabin/people area and above the Tank.

On one of my boats I had to move the exit of the tube higher up the side of the boat to keep it from leaking fuel when I was in rough water.
 
Some tanks have a vented cap with the vent hose from the tank going to the filler neck on the hull. If the cap was replaced with the wrong type, the vent will be blocked. Again, go back to the tank and follow the smaller hose to the side of the boat. That's your vent hose.Hy
 
You must log in or register to reply here.
Back
Top