Fuel system question

[jim56]

Bought a 2006 20' DC and have a fuel system question for the group. I was inspecting the hoses and clamps after buying the boat and I don't see anyway the tank gets vented looking in the inspection hatches. Ever other boat I've owned had a tank vent that was obvious when inspecting the tank and hoses. I don't see anything on this boat that would tell me the tank can vent. What am I missing?


Thanks for the help.  

[yessnoo]

I am not familiar with that specific model but on my 2002 Sv2100 the tank is vented by a hose that runs along side the fill hose which vents through the fuel fill cap. The tank definitely has to have a vent somehow

[gnrphil]

The fuel tank vent is on the port side, usually the vent hose is next to the fill hose on the tank .

[jim56]

Yes there is a hose from the tank that ties into the fill connection a couple inches below the fill cap but I don't see how it vents to atmosphere. Thanks for the reply.

[jim56]

The vent hose actually ties into the fill hose fitting but I don't see a way the cap would let it vent. Thanks for the reply.

[yessnoo]

I just looked at mine. This is the version I have www.perko.com/catalog/fuel_system_components/138/vented_fills_for_1-1_2_hose_-_straight_neck/

If you look at the attached picture you can see a few things. First the vent hose barb is directly connected to the main fill port near the hinge side of the hole. Second you can see on the bottom of the cap is a large oring, In the middle of the oring is a star shaped knob. That fitting can be unscrewed and on the other side of the fitting is a screen. The center of the fitting works like a plunger (perko calls it a surge plug). When pressure is positive in the tank it pushes the plunger up blocking the vent. When tank pressure is negative or neutral the plunger relaxes and allows the tank to vent between the oring and the plastic cap. At least this is my understanding of how it works. Other style perko caps with 2 hoses appear to work in a similar manner. They do make none vented fuel caps which would require a separate vent on the boat. I have seen these under the gunnel lip on the outside of the boat before...looks like a small metal protrusion with a vent screen on the under side. I am sure other vent styles exist as well.



Also it is possible for the screen to get clogged with debris and block the vent which is why it can be unscrewed for cleaning. 

[jim56]

Thank you very much. My cap just screws shut with no visible way to vent. It looks like the factory cap so there is something here I still don't understand. It has the vent hose coming in from the side as shown but no way I can see for the cap to vent. I will check out the Perko caps and see what's available.

[gnrphil]

It should vent to the side like on the picture I posted, separate hose from there to the tank and a separate fill hose to the tank. If that's not the case I can only guess someone has changed it, possibly because the vent got blocked.

[jim56]

The vent hose does tie into the side but the cap has no venting mechanism. I ordered a Perko replacement. It's not worth any further exploration as the Perko is under 50$ and its not hard to change. Thanks for the help. Your suggestion looking at Perko set me on the right path.

[mattmapple]

It sounds like you've already got a good plan with the Perko replacement. One thing to keep in mind, when you install the new cap, double-check the vent hose connection to ensure it's secure and not kinked. Sometimes, a kinked or loose hose can cause venting issues even with the right cap in place. Also, give the vent screen a quick inspection now and then to keep it clear of debris. Happy boating!