I give up. My 86 f-520 with a 460 Manual needed new tanks when I got her. I replaced them both and was told to vent the tanks to each other, so I did. It always seemed like it was always flooding when driving down the road, and always had the smell of gas when parked in the garage. This would stay until I let the pressure off by opening the gas caps. In the middle of an engine swap I came across a couple of boxes on the frame behind the radiator, on the passenger side. Looked this up in the LMC Trucks book and found they were vapor cannisters. For which I took for being a vent box for the gas tanks. So I ordered the cannisters but they did not come with any way to attach the vent lines to. My cannisters were open on top but I can see a 3/16 line below the canisters that runs down the frame to the rear of the truck by the gas tanks. Any one know what I need to connect the lines to the cannisters with????
Thanks for your help,
Rob

 

I have never had one apart, but they have a plastic manifold on top with hose barbs on it. Junkyard here we come.

You will probably still get a gas smell in the engine compartment unless you hook all the vacuum lines from the canister back up to the engine.

 

Thanks, Franklin! That must be where my gas smell is coming from. My gas tank is hooked up to the vapor canister, but I replaced my factory Motorcraft emissions carb with a Holley 4-barrel carb that does NOT come with a bowl vent to hook the other vapor line up to.

I am running a Holley 470cfm Truck Avenger that has a vent tube linking the primaries and secondaries together with small holes in the top of it, so hooking up a vapor line from the carb is not possible. Any ideas? Would running a line from the air cleaner to the vapor/charcoal canister do the same thing?

 

I had an idea, but have never tried it. Instead of hooking the steel line coming from the tanks on the passenger side frame rail up to the charcoal canister, I always thought I could drill a hole in the air cleaner and run a hose from the steel line up to the aircleaner. That way the air cleaner would possibly contain the smell somewhat, and when you are running, the fumes would be sucked in the engine.

In the old days they had vented gas caps, so I guess the fumes just went out around the gas cap.

 

Most canisters have two or three lines or ports to them.

1) Vapor in

2) Vapor out

3) Vacuum valve, on three port types

A line from the tank vent to the vapor in port on the canister to give the gas vapors a place to go.

The vapor out line from the canister is run to the intake vacuum through a vacuum valve which is turned on itself by vacuum. Sometimes the valve is built into the canister itself, other times not.

When the engine is off all the vapors are stored in the charcoal inside the canister, looks just like fish tank charcoal for filtering and most likely is. When the engine is started the vacuum valve is opened and the vapors sucked out.

It is too catch the vapors for many reasons and all good. Vapors burn your eyes, make you sick, and can cause a big explosion. This is very much so when parked in a garage with a gas water heater. Never leave this system out!

I have replaced them before and always buy new ones as the charcoal wears out. Just get any size that is close and has the right number of ports. GM's I think are the easiest to get and cheapest. Try Napa or Auto Zone and pick 5 or 6 to zero in on style or price.

 

Do not hook the other end of the vapor canister to the air filter housing. It is not the same as your crankcase ventilation system. The last thing you need is to hook those lines to your air cleaner. You will have lots of gasoline fumes mixing with fresh air. On a cold morning if your choke sticks open or opens too quickly you could easily get a backfire through the carb and anywhere froma small explosion to an engine fire from teh fumes you would be plumbing directly into your air cleaner box.

Personally on my '86 I got rid of the smog carb and smog equipment. The tanks on my truck are vented on the top and have a ball valve on top so if the truck ever rolls it will stop the flow of fuel, or when the tanks are full the ball floats and the valve closes. Nifty design. Anyhow, after removing the smog equipment the truck sure has a lot more power, and goes a little farther between fueling.

 

I thought about running a venting line at the rear, but you need to have some way to keep dirt and water from getting in, such as a line mounted up high with some sort of filter or something on it. The ball check valve on top is standard for all the tank fittings I believe.
My diesel has the vent lines in the back, and they run a rubber line over to the outside of the frame. Looks like it would get dirt and water in it, but I guess it works ok.

 

I recently put an edelbrock carb on my truck, and just capped off the bowl vent lines. I dont have to do smog checks yet, but I am leaving the parts intact in case that changes. The truck runs fine, no fumes or anything, but it is parked outside all the time.

 

Before "emissions" all carburetor float bowls were vented to the carburetor airhorns with apparently no problems. My '83 F350 with 460 has no external carburetor vent lines and cannisters, just vents to the airhorn (top of carburetor). Came that way from factory. The fuel tank only has a check valve and a short length of hose letting air enter the tank to replace the volume of fuel used; no cannister. I'm pretty sure your tank vent lines should also be open to the atmosphere, not connected together. You've got to have some way to get air into the tanks as fuel is used up.

 

If he had a cannister, then each tank has a small rubber line going over to a small steel line that runs up the passenger side frame rail and it's connected to the cannister.

 

Found this:

<LI type=square>Fuel Tank- All fuel tanks in today's cars are designed to allow for fuel expansion. The expansion space is usually 10 to 12% of the total tank volume. For example, a tank designed to hold 12 gallons of fuel, when filled, would need at least an additional 1 gallon capacity for expansion space can be designed into a fuel tank. The easiest way is to locate the filler neck. An air space is then created at the top of the tank when it is filled. Designing a bulge or dome on the top of the tank serves the same purpose. The air pocket absorbs the increase in volume, as the fuel expands.
Another way to create an air space in the top of the tank is to connect a fill control tube to the filler neck. When the tank reaches a certain level as it is being filled, gasoline begins to flow back through the fill control tube into the filler neck. This causes the gas nozzle to kick off and prevents overfilling the fuel tank. The remaining air space at the top of the tank then serves as the expansion reserve.
The only problems any of these expansion control techniques can create are complaints about bslow filling. Many motorists quickly discover that such fuel tanks fill slowly, or that they never seem to be quite full. That is because the tanks are designed that way. Overfilling, by continually squeezing in a few more cents' worth of gasoline after the nozzle has kicked off, defeats the designed purpose of expansion control.
<LI type=square>Gas Cap- Most people dont relize the gas cap is an emission control device, but it is. In precontrol days, the gas cap's main job was to keep gasoline from sloshing out of the tank, and dirt from getting in the tank. It was equipped with a small vent hole so that the tank could breathe. Air entered through the cap to make up for fuel as it was used, and fuel vapors exited through the cap as internal pressure rose on warm days.
Todays emission control gas caps are considerably different. They are either of a solid construction(venting is provided by other means) or they contain a pressure/vacuum valve. The valve type cap will vent tank pressure if it exceeds 1 psi.It will also allow air to enter the tank if a vacuum exists within the tank. In other words, the valve type cap can vent pressure or releive vacuum as the situation warrants without allowing gasoline vapors to pollute the environment.
The valve itself is a simple double spring arrangement similar to a radiator cap. One spring reacts to internal pressure while the other reacts to external pressure. A plate or diaphragm between the two springs opens and closes to allow air to pass through the valve in the direction needed.
Internal fuel tank pressure can be also vented by means of a three way valve in a vapor line to the charcoal canister. Some ford vehicles do not have a pressure/vacuum releif gas cap. Instead they use a three way valve in the fuel tank vent line to control internal tank pressure. The valve vents tank pressure to th charcoal canister. When there's a vacuum in the tank, the upper diaphragm will allow air to be drawn into the vent line to the tank. The lower diaphragm serves as a safety vent for excessive tank pressure in case the main vent line becomes clogged.

 

Moxy, not all older vehicles were vented through the cap. All my Galaxies have had non-vanted tanks. The filler neck is positioned into the tank in that you can not totally fill it. There is a small air pocket, and when removing the cap after running nearly empty there is a whoosh of incoming air to make up for the slight vacuum.

My Falcon though, had a vented to atmosphere tank and the design (tank is the trunk floor) is such that any air pockets should be minimal. It had a vent tube coming out of the filler neck and winding around under the car then coing out on the passenger side right behind the bumper. When I first got the car I thought it was odd that it only took a couple gallons of gas, but assumed it was full. Wrong. Ran out. The vent tube was clogged and it would take forever to fill. Once I figured that out I took some pipe cleaner and cleaned the dirt and gunk buildup from the end of the vent tube. It would then fill much more quickly.

So, not all early cars were vented through the gas cap.

 

Those are quite old cars. I believe the cars after the late to mid 70's were required to do so.

The point I was trying to make is I would think twice about removing a vapor system as the system is more a safety issue than anything else and if it is functioning the effect on engine performance is zero or a plus.

It just stores fumes when in the off mode and burns them through the intake system of the engine, intake vacuum, carburetor port, etc. when running.

It helps stop explosions when stored inside a garage, eye and throat problems from burning and also just wasted gas fumes. When burned the gas is put to use and the O2 sensor adjusts everything to normal the fuel is not wasted.

Think about how much gas is evaporated over a year of rolling around in a tank, hundreds of miles for most cars and trucks.

Parking lots would choke a person in the 50's and 60's before they started mandating the system.

 

I'm willing to bet you weren't even alive in the '60s. I've been to plenty of parking lots full of '50s and '60s cars (never been to a car show) and have never been "choked" by fumes or even smelled any gasoline odor.

I'm not saying the vapor control systems on new cars are bad. I personally do not leave them on as most trucks I've owned have had emissions stuff modified and/or removed previously so I just get rid of the rest and clean it up so I have more room to work on the thing and have a cleaner looking engine compartment. Less to break is a good thing.

 

Sorry this is so personal, not my intent.

I was alive and well the entire decade of the 60's though.