Collapsing fuel tank

Rice154 · Feb 17, 2020

I’m running a stock 340 with Holley 650 DP in a ‘73 charger. I’ve unhooked the charcoal canister and plugged the line leading back to the tank as the canister is not hooked up to the carb. Noticed the fuel tank is collapsing. I Am using a vented cap. Not sure if the charcoal canister removal did the deed or if the issue existed beforehand. Thanks for the assistance in advance.

69L48Z27 · Feb 17, 2020

If the tank is collapsing and you remove the gas cap and you get a big inrush of air, it’s not vented. I think vented gas caps are for pressure not vacuum, never studied how a gas cap works if it’s vented though.

Mick56 · Feb 17, 2020

Blow a little air into the tank to pop it back out, and then hook the cannister back up.

Runner 68 · Feb 17, 2020

If I remember correctly when we did my son's 72 Duster with a 318 and the canister, we simply cut the vent line to the canister low in the engine compartment then put a small K&N on the line so it could vent.
Canister totally removed. No problems.
I hope this helps.

mopar 3 B · Feb 17, 2020

Rice154 said:
I’m running a stock 340 with Holley 650 DP in a ‘73 charger. I’ve unhooked the charcoal canister and plugged the line leading back to the tank as the canister is not hooked up to the carb. Noticed the fuel tank is collapsing. I Am using a vented cap. Not sure if the charcoal canister removal did the deed or if the issue existed beforehand. Thanks for the assistance in advance.

If the fuel tank is collapsing the gas cap is not vented plan and simple.

Runner 68 · Feb 17, 2020

mopar 3 B said:
If the fuel tank is collapsing the gas cap is not vented plan and simple.

The only problem is that I'm not sure how much a vented filler cap actually vents the tank, in any kind of volume.
Vent it from the line going to the canister as well. Much bigger orifice.

Aeronet · Feb 17, 2020

Use a fuel filter to plug the tank to canister line. I do ('73 Charger). No collapsing gas tank on mine. Vented gas cap.

72RoadrunnerGTX · Feb 17, 2020

The canister line from the fuel tank is the fuel tank vent, can’t plug it off. The correct filler cap is not vented. If you are running a carb without a specific timed canister purge port, tee the purge line to the PCV line, insert a restriction of about .030” in the purge line. It won’t purge at the original rate but will be somewhat functional as originally designed.

Ernie ingling · Feb 18, 2020

69L correct vented cap is to remove pressure not vacuum. So pop out tank and hook up char. canister. It will NOT reduce horsepower

Collapsing fuel tank

Rice154

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69L48Z27

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Mick56

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Runner 68

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mopar 3 B

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Runner 68

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Aeronet

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72RoadrunnerGTX

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Ernie ingling

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