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Tech Question
Frank Lundholm, Cookeville, TN, 71 Plymouth GTX 426
My gas tank makes a "gurgling" type noise from expansion or contraction. Sometimes it does it when warming up the garage or when sunlight shines on the car. It also releases pressure or vacuum when the gas cap is opened.
The vehicle is modified with a 750 cfm Demon carburetor and NO original equipment, hoses, or canisters remaining in the engine bay. The small tank mounted in the left rear wheelwell appears to be in excellent condition and all the rear connecting hoses are new. The 3/8" fuel line goes to a mechanical fuel pump and the 1/4" "return" line is connected to a metered bypass port on the fuel filter. The 5/16" "vapor" line is plugged, just below the firewall.
Question #1:Could you please explain how the original fuel tank system is supposed to work?
Question #2: Can you advise the best way I can utilize the existing system for performance? Maintaining stock apearance is not necessary.
Question #3: It seems like the "vapor" line should be vented. If so, what would be the safest way to do this and avoid the smell of gas inside the vehicle? I thought of venting it into the carburetor breather, but worried about a backfire.
Thank You
FYI: I had to restrict the "return" fuel line by-pass port to .030"
because the standard size orifice on the filter lowered the fuel pressure
too much.
Frank-
I've described the operation of the stock vapor recovery / charcoal cannister system several times, and, since you've already trashed it, I will skip that part of your question.
The gas tank's gotta be vented somehow - that, as you are aware, is what you're missing. There are a few ways to accomplish this. First, you could duplicate the stock pre-emission-era factory-type setup. This typically consisted of a hardline that reached as high in the car as possible (into the C-pillar, usually) and the looped back down. Frequently this terminated in a rear frame rail, where the vapor would escape, and any errant solid fuel would safely evaporate (by disapating over the large area inside the rail) instead of creating a liquid leak.
I agree with you - ventimg inside the engine compartment isn't the best idea. So the other idea would be a simple vented gas cap. if this produces a solid fuel leak under hard accelleration, likely with your GTX's low, rear-mounted filler neck, simply use, instead, one of the common "pressure-vacuum" (i.e., built-in check-valve) type caps. These, however, can permit more fuel presuure variations, so, unless you've wisely installed a f.p. regulator, I'd suggest one of the first two options.
Having done this, the expansion tank no longer does anything, and can be removed.
If an stock emissions-era filter's return orifice lowered the fuel pressure too much, your fuel delivery system is marginal at best!
Rick
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