Plastic gas tank venting questions

[jeswinehart]

Has anybody had a problem with those little vent cap topper things ?
I had a couple on my first gen Tecate but to be honest they got knocked off in short order so other then keeping them my tank I can't answer my own question which is,,,,, since they only let air draw in, if pressure builds up inside from sunlight heat dose the tank just swell or is pressure simply pushed thru the carb ???

[El Camexican]

I think mine has a check ball in it. If I park in the sun and go for tacos I can here air escaping from it when I return. That said I always shut my petcock off when I park, so the tank (which is black) builds up heat fast.

Never had it come of, but I did have to heat the hose with a lighter to get it on as It was a size smaller than the nipple on my cap.

[jeswinehart]

Perhaps Nico if the pressure builds up slowly it vents back out the cap ??? I am going to buy a tee and some other fittings and do a science fair type of testing on one tomorrow. Pressure test it I suppose would be best wording.
I don't think the ones I have are spring loaded but just rather a ball,,, I may cut it in half after screwing around with pressure testing.

Thanks Nico, john

[oscarmayer]

that cap is exactly what it is supposed to do. allow air to vent out. if you go online and buy the Chinese ebay specials they are FAKE. there is no check valve and it usually does not allow for proper venting. Go on, ask me how I know. ;-)
go to the dealer and order one for $15-$20 behind the counter. they will have a check ball you can hear rattling. it will allow air and pressure to escape from the tank, w/o allow fluid to escape easily incase of roll over. I recommend you zip tie it on. my son is always gets caught on his shirt when rolling it out or into the toy hauler and pops off. Zip tie helps keep it on better. :)

now, the cap could also be bad and not allowing pressure to vent. check that. always clean your parts include the vent tube, check valve and the cap.

[El Camexican]

Perhaps Nico if the pressure builds up slowly it vents back out the cap ??? I am going to buy a tee and some other fittings and do a science fair type of testing on one tomorrow. Pressure test it I suppose would be best wording.
I don't think the ones I have are spring loaded but just rather a ball,,, I may cut it in half after screwing around with pressure testing.

Thanks Nico, john

Yours looks just like mine aside from the color. Mine rattles when I shake it, I would think if it does have a spring its very weak.

[oscarmayer]

^ yep you got a real one. the Chinese ones do not rattle. they are just a fake piece of allow machined to look like one. once in a while you'll get lucky and find one with a hole in it that does some sort of venting.

[onformula1]

IMHO these are the only way to go, I only use these & have one from 1990 that still works.

They vent, but don't leak fuel if the trike is sideways or upside down, they don't rot, or stick and they hold the cap when refueling.

Free Flo No Slop Gas Cap Vent Hose

http://www.motosport.com/free-flo-no-slop-vent-hose

They come in 5 colors.

Here is the newer model that swivels- (Never tried this model)

http://www.motosport.com/free-flo-no-slop-swivel-vent-hose

Do a google search, many companies carry them.

I use stainless safety wire to hold it on the cap. (Its not needed, but I do it, don't ask me why..LOL)
I use a 3M zip tie on the other end.

[jeswinehart]

These, or at least the ones I have are a POS. Holds pressure at 1 inch of w.c. up to 18 inches of wc.
It never did try to vent any build up of pressure what so ever.

[jeswinehart]

The Mrs. and I went out and done our shopping and running around. Left the house at 11 am ish when garage was at about 55 degree.
Got home a few minutes ago and it is 81 in garage.
Left the manometer at 9 + 9 inch's of w.c at 11ish.
pressure climbed with temp increase ,,, a lot.
I WAS going to supply these vent caps with the tanks we are doing. They are now heading for the trash.

[oscarmayer]

Good. Get some real stuff.


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