How to test if the gas tank has adequate venting?

Rafs-T-Type

Not so Senior Member
I have been trying to figure out why my car is starving for fuel and the tech at magnafuel said first thing is to make sure you have at least 1/2" vent. I was wondering if there is a way to test to see if this is the culprit before I go and drop the tank and what-not. It's pretty ghetto, but I was thinking about using something to hold the flap open in the neck and taping some rags over the fill tube and seeing if it makes a difference on a run. Thoughts?
 
Does your car release a lot of pressure when you take off your gas cap? Just loosen your cap and drive it and see if it still starves for fuel.
 
Sometimes you really have to wonder about tech lines and the "experts" giving info, a 1/2" vent line, give me a break? :confused:

The 5/16" GN vent line has worked well into the low 9's.

Check your existing vent line to be sure it is open, and not plugged with carbon like I have found a few that were.

On a GN, the most fuel supply issues are not enough voltage at the pump, lines crimped or not adequate, and the no. 1 issue, a weak or bad fuel pump.

If you want to verify a vent line problem, loosed the fuel fill cap, and try that. The flap inside the fill tube is not air tight.

Also, if the vent line is plugged, when you loosen the cap after driving it, you will hear air rush into the tank.
 
Sometimes you really have to wonder about tech lines and the "experts" giving info, a 1/2" vent line, give me a break? :confused:

The 5/16" GN vent line has worked well into the low 9's.

Check your existing vent line to be sure it is open, and not plugged with carbon like I have found a few that were.

On a GN, the most fuel supply issues are not enough voltage at the pump, lines crimped or not adequate, and the no. 1 issue, a weak or bad fuel pump.

If you want to verify a vent line problem, loosed the fuel fill cap, and try that. The flap inside the fill tube is not air tight.

Also, if the vent line is plugged, when you loosen the cap after driving it, you will hear air rush into the tank.

I never get that vacuum when I go to fill up. There should be plenty of juice at the pump with the 4 gauge wire feeding it. -10 fuel lines. I'm just running out of ideas here. The pump is a magnafuel 4301 that people have gone 8's with. It seems to be rising 1:1 alright, just not very smoothly. I'm running out of ideas. :confused:
 
I ripped my fuel sender apart recently and found that the little 5/16" vent line is also orificed inside the tube, about 1mm or so.

Currently running a vented gas cap instead of the factory vent line. Works fine.
 
no room for a vent with this contraption...

DICKDP3.jpg
 
Autozone has them normally in stock. Part # 6817 vented CST fuel cap $8.99
that's the one, IIRC. Seems to be vented with a one-way check. Lets air in but doesn't let vapors out. If the fuel tank warms up it will make the "rush" sound when the cap is loosened, but not when the tank is cold.
 
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