Fuel System

[gsmobayed]

I have a 69 Roadrunner, and have noticed that my fuel tank is collapsed, when I have little fuel left. As soon as I remove the gas cap, it pops back into shape. Has anyone experienced this, or have any suggestions ??
Std. mechanical fuel pump
Stock tank
Non Vented gas cap
Edelbrock 750cfm carb
Any input is greatly appreciated!!

 

[dbowperson]

Sounds like you need a vented cap at least. That's a pretty nasty vacuum that's being formed in the tank. I believe there should also be an overflow vent in the filler neck which could be clogged.

 

[Northwest]

Even though I have a vented cap on my 71, I noticed a 'depressureization' when I take off the cap. Nothing caving in like you described.

Having a collection of vented caps - I tried anohter one and found that it fit differently - it didn't quite snug down as tight and I didn't have the same vacuum build up.

There may be a couple of different styles of caps / filler necks that don't work right together. I don't know for sure, but just adding my relevant experience.

 

[Meep-Meep]

Yeah, I'd agree that your vent is restricted. 69 RR didn't have a vented cap originally (as I recall) so go to the front of the tank and find the 1/4" line that loops into the trunk and clean it out. The section of hose that connects the fuel sender is probably deteriorated and needs to be replaced.

 

[gsmobayed]

Thanks for all of the input......I will inspect the vent asap.

 

[Coronet 500]

If you have two coming out the front of the tank the one closest to the center runs along the top of the tank to the back. The other goes in about 2", both are open ended and don't turn up or down. If one is covered by fuel the other should still allow air into the tank.

 

[Meep-Meep]

If you have two coming out the front of the tank the one closest to the center runs along the top of the tank to the back. The other goes in about 2", both are open ended and don't turn up or down. If one is covered by fuel the other should still allow air into the tank.

Oh yeah, the 69's have a slightly different vent system than the 68's.