Nitro Fuel Vent Caps

[Dan Maier]

I just purchased a used Nitro 2000dc. When trailering I get some fuiel spilling out of one of the Fuel vent caps on the side of the boat (other side of of boat from the filler caps). These seem to be used for air to escape the fuel tank? I was told to open them when fueling and screw the cap on when done but when screwed in dont completely seal. Can these be replaced with just any Marine thru-hull fuel vent? How are these meant to work?

 

[Dan J.]

They're the older "burp" valves. Most mfr.'s have switched to a vented fill neck to relieve the burp. Check your caps for a good seal and replace if necessary. I can't remember if yours are chrome or black plastic (I suffer from CRS :lol: ), but check the link I added and either retrofit or replace worn caps. You need a burp vent on a closed system or a rupture somewhere will happen. Good luck!
http://www.marineengine.com/products/accessories.php?g=501

 

[Dan Maier]

So should the caps be completly sealed after fueling or should they still act as a vent? It looks like the one for the reserve tank completly seals if it where screwed all the way on but the main tank can only be screwed on so far as i looks like it still vents when screwed down.

 

[Dan J.]

They should be similar, if not identical, and screwed down when filled then backed off a few turns while filling to vent the rapidly shrinking air void. With a closed system you should be able to contain acceptable pressure to keep the system primed and "burp" or expel built up pressure above the required. One valve almost always will burp before another if both are purge valved. (Think one way burp flap.) Some units have only one (single tanks usually) and to be honest, that long ago I can't remember on your unit. I do remember that they were black and/or chrome. If you have to keep priming your pump ball during use, at least one is probably bad, barring any other air leaks. I hope this helps. Good luck!

 

[Dan J.]

Update bump.

 

[Dan Maier]

So I spent some time on this yesterday evening. After closer inspection the caps do not screw all the way down so it looks like they do vent even when screwed down all the way. Both vents are identical but looks like the old owner put some teflon tape around the threads on the reserve valve so when the cap is on there is no room for it to vent as it should. They are chrome with black caps (but who know if the caps are the correct ones). I purchased two new vents with caps and will redo them properly. My concern is ....... what keeps fuel from coming out these vents when sloshing aound while in tow and on the water? They are the 570 model in the link below!



http://www.cgedwards.com/Perko/pko305-16.html

 

[Dan J.]

The vents will not completely seal off the fuel supply. When closed they will retain enough back pressure to keep prime, but when excessive pressure builds, they will still vent or "burp". "Closed" is a releative term for these. Restricted and unrestricted is a better description. Some people will cap them tight, afraid of water intake, however it's almost completely unnecessary when they're working properly. You may just want to strip the threads down to chrome and replace the caps. Then just unscrew to fill (so you don't get a gas shower!). Then screw caps down when finished to "close" the system.

 

[Dan Maier]

Dan - You have been very helpfull on this topic! what do you mean when you say ...."You may just want to strip the threads down to chrome and replace the caps". Is there a way to just replace the threads and caps without taking the vents out (maybe a trick of the trade).

 

[Dan J.]

Both vents are identical but looks like the old owner put some teflon tape around the threads on the reserve valve so when the cap is on there is no room for it to vent as it should.

Unless you suspect the vents are bad (getting showered when fueling or a water ingestion problem) I'd strip the teflon tape off and put the caps on as when stock. Again, you really don't want a completely sealed fuel system without some sort of a relief incorporated. You will rupture to vent somewhere along the route if you do. (i.e.: pump diaphragm, primer ball....wherever the weakest point is.) Gasoline is very unstable and volatile (rapid expansion & contraction), so a relief is dire for a properly working fuel delivery system to work. If there is any reason to suspect the vents are bad, it's much cheaper (and very easy) to replace over repairing any damage that may incur. (And then you'd have to replace the vent(s) anyhow.) Good luck!

 

[Dan Maier]

Dan Thanks again for all the help! The reason he used teflon tapes is the plastic threads are messed up on both the vales where the caps screw on. I will just replace them both! Thanks again!

 

[Dan J.]

No need for thanks! Feel free to ask anything around here and you'll get replies from a number of very knowledgeable folk. Just don't ask for the last piece of chicken. You might lose a finger! :lol: