Gas Tank Venting

This is so easy a cave man can do it. Go to a motorcycle store and ask for a gas tank check valve or vent tube. They are super easy and this is what I have on mine.

 http://www.motorcycle-supersto...minum-gas-stop-valve

I wonder if I can get one of those set up under the seat with a suction fan to exhaust the fumes..

I use a small PCV valve in line with the tank vent hose and also add a tin gas filter under the front wheel well with a loop in that hose. The filter captures and gas and returns it to the line / tank.

Are you saying that you are passing gas with the windows up?

Vent it back to carbs - initial "venting" will lift you off the seat and "ignition" will push you back in seat!

This caveman has a question.  I bought the part Rusty was talking about for $6.00 at the local Cycle Gear. I went home and pulled the hose out of the hole in the trunk that leads to the right side fender wheel and was expecting to see a plain ol' fuel line.  Stuck in the middle of the hose was a small white plastic one-way valve.  I pulled the hose off the tank spigot and checked to see if the valve was working. The valve was set up to allow air/fuel to flow out of the tank/line (hence the smell) but no air/fuel would be able to flow back into the tank. 

I thought that the line was to allow air back into the tank so as not to create a vacuum and the new check valve was to keep the fuel/fumes in but allow air to be drawn into the tank?

This caveman is confused. 

I solved the problem by changing my driving habits after a fill-up: I would only turn right for the first hundred miles.

Then I ran my hose longer, under the running board and to the rear wheel.  Now I don't smell it as much.

You are RIGHT after all.

Robert, they had it backwards. Some guys don't use a valve at all, they just put a couple loops in it. I'd recommend a valve though, I've seen tanks emptied by self-siphoning without it.

The installer getting it wrong is what I was hoping for.  I added the valve and a little longer hose so I could put a loop in it.

Thanks everyone.

That ain't gonna happen!!

what size is the breather hose and what about foam in the tank to control slosh ?

I wouldn't put foam in a street car tank. It breaks down over time and will clog your filters. If you're that concerned about it, have the tank cut open and have baffles welded in.

These look like a bargain, not sure how well they would hold up tho.

http://www.ebay.com/itm/10pcs-...;hash=item2a3fde7433

Gary

I installed a PVC check valve and am thinking about taking it out.

The valve lets air into the tank as the gas gets used but doesn't let gas (or pressurized air) out.

One time I filled my tank really full and the expanding gas caused the top of my tank to bulge up.

Robert, gas fumes have been an 18-month battle for me, although I think they're finally under control. Here are some things I've learned and done.

In my VS, gas was leaking both INTO the trunk and out the end of the vent tube under the car.

GAS CAP - This should be the unvented type, since the tank has a dedicated vent line in the filler tube. But my genuine Chinese 'unvented' cap had plenty of 'vents' that were letting raw gas spill onto the carpet in the trunk. At first, I thought it was just a leaky gasket, so I replaced that with a thicker one that sealed much better.

But the design of the cap lets gas splash up behind the gasket and out around the rim. There are little tabs that hold the cap onto the filler neck. Next to the tabs are holes where the gas escapes. I sealed off the little gaps inside the cap rim with glue (JB Weld would have been better). I first tried finding an 'unvented' cap that was actually unvented and fit my tank, but with no luck.

WRONG SIZE VENT LINE - The rubber tube connected to the vent nipple on my tank was way too loose. And there was no hose clamp installed. The tube barely stayed on the nipple, and this loose fit let more gas leak into the trunk. It turns out the right size hose for my tank is 5mm. In any case, make sure it's clamped on tight.

LONG LOOP - The original VS vent line had just a simple loop under the car. Once I stopped the leaks inside the trunk, I realized most of the fumes were coming from gas pouring out of the vent line and dripping all over the sides of the wheel well. I added a long loop INSIDE the trunk and this stopped almost all of the fumes. Gas may spill into the vent line, but usually not enough to fill up this loop and overflow under the car. Any gas in the loop gets sucked back into the tank as you drive.

SECOND LOOP UNDER CAR - Occasionally, the long loop in the trunk wasn't long enough and gas would still drip under the car. This week, I got serious and added another loop under the car, with a fuel filter in the loop to keep raw gas from flowing out (the filter is installed with the flow arrow pointing back into the tank).

The loop under the car can be positioned way up at the top of the fender where it is higher than the filler cap. I also led the output end of the loop as low as I could get it, so any gas dripping goes right to the pavement and not along the inside fender walls. In the photo, the line coming in from the right is from the trunk.

I'm not entirely convinced that gas will flow in only one direction through those cheapo fuel filters, but I like the karma of that arrow pointing defiantly back into the tank.

I've got a similar gas cap problem. The gas in the tank sloshes up to the vented gas cap and and releases fumes if the tank is too full.  I haven't been able to find a cap that isn't vented so my fix until I find one is a ziploc bag and a rubber band. Sucks but works.  Better than the gas smell anyway.

I purchased a vented cap and unvented it! 

Mitch,

The filter will flow in both directions, whether it's a cheapo or an expensive German filter. The flow arrow on the filter is so that it filters correctly when used in a fuel line (deposits dirt on the outside of the pleats, not on the inside). It's isn't a check-valve, so it isn't going to stop the fuel from sloshing out.

You can buy a check-valve, as many of us have, at your friendly local auto parts store (FLAPS). They're usually on the "HELP" turnstile, and are generally about as big as a stack of 4 or 5 dimes, with nipples on each end.

The check valve isn't perfect, as it only allows air in to make up for the fuel you are pulling out by running the engine. When fuel comes out of the ground it's cool- when it warms up, it wants to gas off (see what I did right there) and creates a pressure in the tank. I've heard of people's needle valves in the carbs being overwhelmed with the pressure, but I've never experienced it.

Ideal would be a real charcoal canister set-up. Angela Lane advocated for pulling an appropriate sized canister off a car in a "you-pick-it" salvage yard, but most of us haven't gone to that much work. I might, as this is the best (OEM) way to deal with fuel vapors.

Good luck.

Stan, I sort of suspected that the filter wouldn't stop gas flow. I've never heard of any 'miracle one-way paper' that will do that. I guess some filters do incorporate an internal check valve.

But the filter is a sort of inexpensive 'expansion tank' that must fill with gas before any will overflow out the end of the tube. I'm hoping this setup has enough capacity to capture any gas that makes it to the filler neck, and the see-through filter will let me see if it's working. This setup should vent any pressure buildup in the tank, though.

And, I'm thinking green here. With the smugness of a Prius driver, I know that any gas dripping from my car onto public highways will be as free of particulate contamination as Chinese technology can make it.

Mitch - Thanks for your detailed attempts to fix your issue.  I did change my fuel line to a new one, added a high loop, and a one way ATV/Motorcycle tank valve.  I'll check my gas cap to see if fuel leaks form there.

Thanks again.

I am going to remove my one-way check valve because of the tank bulge thing I mentioned above and the possible issue Stan mentions.

I am thinking of putting one or more 360 degree loops in the hose up under the fender top.

I got one loop under fender and still spill gas on left turns with full tank . I think loop has to be high up next to filler to work . I need to buy a longer hose to try it , was going with check valve until I read your reply . Thanks for info , tired of only taking fast rights and slow left turns

Spyders usually don't have a vent, they have a vented cap. Maybe that would prevent the tank from bulging?

Angela is right, the best way to get rid of the gas smell is a charcoal canister.