Fuel Vent Line Question?

[cudacarl]

I have a '73 'cuda 340. The engine is modified with edelbrock intake ,demon carb lager cam etc. When i bought the car the charcol vapor cannister was already missing and the vent line was plugged under the car. I'm going to be installing a new gas tank 3/8 sender and 3/8" fuel line and would like to properly take care of the vent line too. Can i get away with just leaving it plugged or should i some how hook it up? The way i have it could it cause vapor lock?
Thanks-

[dwc43]

The way you have it now it'sa wander it runs right at all. The plugged vent can also expand the tank on hot days to the point of rupture and it effects how the fuel pump pulls fuel from the tank. A 3/8 sender is too big for your 340. Unless it's an all out race engine just replace it with the stock 5/16 cause your just wasting your money. If you think you have a fuel problem it's that plugged vent line. Either get another canister and reinstall it or just unplug it and maybe add a small filter too it so it does not plug up with dirt.

[cudacarl]

I was dealing with cuda66273 back in february on this. I sent him my engine specs and he came up with the demon carb and carter stirp fuel pump because i was starving for gas. I tried to get away with the 5/16's but at top end it still starves thats why i'm going with the 3/8. If i put the cannister in should i just run it to a vaccuum source on the intake.

[dwc43]

Yeah, you could run it to the intake. It was basicly attached to the carb at the throttle blades anyways so it should not make a difference.

[cudacarl]

The gas cap is the locking kind and it doesn't seal all that good thats probably why it still ran. I think i'll try the small filter on the end if the line deal because i have a coolant recovery tank where the cannister should be and a new cap.

[dwc43]

That should work too or you could plug the line and use a vented cap, but my guess would be that you would want to retain he one you have.

[John Kunkel]

The original fuel tank filler cap used on cars with the charcoal canister is a pressure/vacuum cap. It will relieve any pressure over about 1 psi and will open at a vacuum of around .1 psi.
Since the cap will both vent pressure and relieve vacuum, plugging the vent line to the charcoal canister won't have a noticeable effect but the slight vacuum that occurs with the plugged vent makes the fuel pump work harder and isn't good for an efficient fuel delivery system and could cause vapor lock under severe conditions.

[cudacarl]

Being i'm running a Demon carb with no provision for the vent line and the only port on the manifold is being used for the power brakes, whats the best way to go without using the charcol cannister being i don't have one and don't really have the space for it?

[dwc43]

Either plug the line and use a vented cap or put a filter on it and let it be. I vote for the latter, but I have done both before as well as reinstalling the canister too.

[70Barracuda]

The sending unit will have an extra nipple for a vent tube. Mine does. For some reason the venting gas cap I have wont vent!!

[dwc43]

Stopped up??

[cuda66273]

" I tried to get away with the 5/16's but at top end it still starves thats why i'm going with the 3/8. If i put the cannister in should i just run it to a vaccuum source on the intake."

Yes and it will continue untill you give it adaquate fuel delivery, the 3/8th line is the correct upgrade.

"A 3/8 sender is too big for your 340."
Broadband statement for not knowing what the engine and fuel requirements are...don't you think?

I don't want to get into another Pissing match here with you DWC but that statement is not based on facts.

[dwc43]

Geee, never knew we got into any pissing matches. I based that on what he said. It sounded like a fairly mild build by the way the described it.

[cudacarl]

Hey cuda66273 can i leave that line plugged. Like i said i don't have room for that big cannister or is there something else i can use instead of it? I'm putting the 3/8 sender in the tank and i think it has a provision for a vent line. Can i do something with that? - thanks

[atoetly]

At my age everything is a pissing match....you should see my shoes after 3-4 EBL's LOL....

DWC probably works on more stock stuff than we do....we junk all that stuff and add a vent line that is 1 line size smaller than the outlet to the pump.

-08 outlet would get a -06 vent

Do you need to run all that cannister stuff for nostalgia purposes or is this more of a HotRod?

As Tim mentioned the 3/8 kit comes with a vent tube in the mounting plate and can be vented anywhere convenient.

[cuda66273]

Oppps....I see atoetly was playing with my computor and I seem to have posted my reply with his log - on....

[dave571]

I wouldn't put it on direct vacuum. That's not quite how the canister system worked(when you had it)

Even on a modern FI OBDII car with a sealed vapour system, there is a certain amount of bleed off, and it is never under full vacuum.

Run the vent somewhere. higher than the tank, and stick a fuel filter in the end of the tube. On cars that predated carbon canitsters(in general, including brand X) the tanks are vented to atmosphere, usually via a vented gas cap.