69 Road Runner, restored, new tank, oem thick retaining ring, vent lines are not reversed in the tank (scoped it to see), exterior vent lines are new and hooked up properly. When I drive in hot weather, engine hot, then stop and turn it off it sometimes burbles or bubbles (sounds like boiling fuel but s not hot enough to do that) it will barf out some fuel from the vent line sending unit area (not exactly sure where as I can't physically jack up the car and get underneath it fast enough to check). It will stop making bubbling noises when I open the cap. When I do open the cap,when all this is happening it blows out, pressure is definitely building in there some how.

Please help. Anyone else experience this?

Thanks in advance for your replies

I ain't familiar with that tank vent system but just a basic Q, is the tank vented to the atmosphere or does a line go back up front to a charcoal canister or? I'm thinking the '69 MY would not be vented to the atmosphere with gov't emission regs of that era.

If you can drive the car with the tank fuel cap off and this doesn't happen, I'd start with the cap as the source

69 rr would be non vented cap. Are you running a fuel return line?

Fwiw I'd swap the vent lines, quick and easy to try.

It's Non vented cap.

If one drove without the cap the fuel would come out the back buy the gallons. (License plate area for those not familiar with a 69 road runner.)

The lines are correct. Yes spectre was known for reversing the lines in the tank but this is both not a scepter tank or reversed inside.

There are no return lines.

If one reversed the the lines the short one would be hooked up to the short one in the tank, fuel would come out for sure then.

What it is, is confusing...?

did you blow air thru the new vent lines to make sure there is no obst.?its a simple system,gotta be a simple fix witch can some times be the easiest to over look.my stock tank had check balls in it my spectra tank didnt.if it has the check balls you may have to use suction to check for obst.

Release the cap for a moment when you park it, I bet you have a nearly full tank and the vents get gas in them. when you shut the engine off you no longer have the demand for gas and it builds a little pressure for some reason be it gas drain back or something and it burps gas. Run the tank down some and it will vent vapors instead and stink the garage up.

Your not using the 1/4" return nipple on the sending unit as a vent line are you?

A bit of pressure during the hot weather and actually some vacuum during the cool weather is normal when you open a pressure/vacuum fuel cap equipped gas tank. Not sure about your 69 other than I am betting it is vented in the rear trunk/rear frame rail? Pressure vacuum cap is too late for a 69 I am thinking. I don't have 69 FSM to look at for ya.

If you are using that return nipple as a vent, stop and cap it. It is not a vent line. Good luck.

If he has the 5/16 sending unit they don't have the return on them. Crawl under the car and look for gas stains.

Sounds like a common problem. Interesting thread here.

http://www.forbbodiesonly.com/moparforum/threads/road-runner-vented-fuel-cap.113987/

69Hemibeep is correct, It is the 5/16 sending unit and yes it does not have the return. As for gas stains it is hard to determine where exactly it is coming from as the fuel travels the lip of the tank. At first I thought it was the lock ring but I have installed the oem one the sender. After that I scoped the vents on the inside of the tank and they are oriented correctly, and the lines are hooked up as they should be. Confusing indeed..... It does indeed vent vapors and stink the garage up after the initial little bit of barfing up fuel...

For the other posters, it has 1/4 tank of fuel in it.

I will try and blow through the vent lines.

At a 1/4 tank the fuel is nowhere near the vent lines? Unless you have a new less than accurate sending unit. If it is a vent its going to be the short J shaped one that clips to the support above and should connect to the long tube in the tank.

This is what I think too. When I pull into the garage the car goes on quite the incline which probably causes whatever has is in he tank to slosh all the way to the back where the long interior line is that connects to the short J hose on the outside. Maybe because the everything is hot there is a slight vacuum and when it sloshes to the rear that one vent line sucks up some gas and then proceeds to spit it out.

Next time I park I will back in to keep the fuel away from that one line and see what happens.

I'll report the results.

I'm also going to check and see if the short j tube has the clip and is connected to the subframe. Maybe if it's hanging a bit that could be an issue too. I didn't pay enough attention to it he last time I was under the car.

The sending unit is a good one. Works accurately. It was bought from mopar in 1996 but only put into service in 2015

Okay, I took a blow gun and blew through the vent lines and they are clear and hooked up properly.

The tank seems to be pressurizing and when it does push fuel out it is coming from the small exterior vent line (closest to the sender) which is hooked the the long line inside the tank.

What is going on?