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Fuel vapor line
So I am in the process of cleaning my tank after it has been sitting for the last 10 years. I am wondering if the vapor fuel line that runs to a canister in my engine bay is neccessary for normal operation of the car. The canister has the remnants of another larger hose coming off of it that rotted away long before I ever got it. What is this whole system for and will my car work perfectly fine without it? If I do delete it, can I just cap off the outlet on top of the tank or should I leave it open to breathe? I am replacing all of my fuel lines and would like to not have to replace this as well if it is not needed. As always everyones help is greatly appreciated!

<img src="http://www.7173mustangs.com/gallery/1_12_09_14_10_32_45.png" />

- Nik
there is a REALLY long answer for this and it was covered on the forum a few times, but.

Yes the vapor line is needed for proper operation when using the factory gas cap. The 71-73 fuel tank uses a sealed cap. the tank must be vented to prevent the tank from implosion as the fuel is used up and replaced with vacuum. think of it as drinking fruit juice from a Caprice sun bag you suck on the straw and eventually the bag collapses.

So you can use a vented fuel cap and then plug off the vapor system if you want.

the whole system exists because of emissions laws starting in late 1970 that required a lower amount of Fuel vapor escaping into the atmosphere.

under stock operation the vapor line exits the top of the fuel tank goes through the transmission tunnel up the firewall , a hose then connects the hard line to a Charcoal canister the canister then has a hose going to the OEM carburetor Fuel Bowl vent and a paper tube connects to the air cleaner base. a filter inside the Base protects the canister and vapor system from a back fire through the carb.

when the engine is running at idle, a slight air flow is created through the canister that goes back to the fuel tank, moisture from the empty space in the fuel tank along with fuel vapor is then sucked out of the fuel tank and down into the carburetor body.

this helps prevent internal fuel tank rust that can rott the tank from the inside out over many years. the extra fuel vapor is also controlled and contained, reducing emissions when the car is parked, it also prevents fuel evaporation that occurs as a car sits.

the system does a lot of good and makes the air a little cleaner.

that said you can run without the vapor system you can cap it off but you must replace the 71-73 fuel cap with an earlier vented 1970 cap, to allow the fuel tank to equalize pressure as the fuel is used up.

Depending on local emissions laws removing the system may be illegal and could fail a road inspection in some states.
you can get around that by registering the car as a classic or antique but you may be limited to 2000-3000 miles a year in driving.

if you ever approach a classic parked and get a faint whiff of gasoline you can bet the fuel vapor emissions system is missing, broken, or was never installed if the car is pre 1970.
Thanks for the very detailed reply. I did a search on the forum for this before posting but came up empty handed to my exact answer. Very good info!

<img src="http://www.7173mustangs.com/gallery/1_12_09_14_10_32_45.png" />

- Nik
this is what the canister looks like. The blue one.
the black canister is the vacuum canister for the Climate control vacuum motors.

[Image: 100_1291.jpg]

for 1973 the canister was a slightly different shape and they changed the mounting point from the side engine apron to the passenger shock tower.
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