I have a '73 Challenger that I transplanted a 440 into. I trashed the charcoal can but never connected the steel line that comes from the gas tank to the charcoal can to anything. The line is still there just open to the air. I notice sometimes when I open the gas cap there is a pressure difference and air rushes in. Should I connect the vent line to a vacuum source and if so any suggestions where? Thanks

Connect it to the valve cover breather.

Thanks- I'll give it a try

I would try a vented gas cap.

I thought of that but wanted to keep the stock look. Thanks

Well, if you have air rushing IN then hooking the line up to a vacuum source is just going to exacerbate the problem I would think.

If the motor is running fine, don't worry about it. Both my cars do it when I open the gas cap.

I would still hook up the old vent line to the breather just to keep crude out of it.

I wouldn't vent the cap either unless you want gas running down your quarter when corning.

When you are having trouble, stop and take your gas cap off and stuff a rag in there temporly. See if the problem goes away, I bet it won't.

Thanks for all the answers but I got another question. Would NOT running this line to a vacuum source inhibit the flow of fuel? I've experienced what seems like vapor lock on hot days and started to wonder if in fact the problem was this non-connected vent line. What do you guys think? Thanks Again

Need to know lot's more, are you using a electric fuel pump? What kind and what size lines and filters are you using? Tell us more.

If your tank is creating a vacuum effect the pump is struggling against that to pull fuel. Think of it as sucking air through a straw, now put your finger over the end of the straw and try again.

If the line going to the old canister is blocked that wouldn't help. Go back by the tank and pull it off and see if you can blow some compressed air through it. It could be the rubber line back there is collapsed as well. I use the old canister line to vent my tank, I just stuck a small filter in the end under the hood to keep the garbage out. If your car is show quality then that may not work for you.

Didn't you ask this question on another forum? I responded to it a few weeks ago. Weren't you trying to use the vapor line as a fuel return?


If you are getting a vacuum in the tank, the valve in the vapor separator is rusted shut. The valve should vent the tank to the charcole canister. Soak the separator in EvapoRust and the valve should free up. Your problem should go away.

It's hard for me to tell if it's a vacuum or pressure when I take my cap off. I have run both of my cars in extreme conditions and have plenty of fuel delivery with stock fuel pumps and a factory style return line, like the hemis and 440/6 used. Works great with todays crap gas.
Like I said above, next time the car acts up, take the fuel cap off to make sure the tank venting is or not the problem, which I doubt.

Thanks again to all the suggestions. Let me see if I can answer all the questions. Fuel delivery is through stock lines via a mechanical pump and in-line Holley fuel filter. No I didn't ask this question before but sounds like someone else had a similar question. And finally, yes The next time I have the car out and it starts to "stumble", I'll pull the gas cap and see what happens. Oh, and I'll blow the line out tonight and see if any dirt or critters come out. Thanks Again to all