Factory EEC systems, differences in fuel tanks, vapor lock, fuel return line or not

[71CHEVYSHORTBED402]

There's another thread on return lines, but I didn't want to hijack the thread with...................

I can pretty well only speak for a 71, and a 1970 with EEC. 402 with 400TH to be exact, though it may not matter too much.

Is a 1972 fuel tank the same as a 70-71 EEC tank? Not clear where there's a difference, but I know a 70-71 EEC gas cap differs from a 72 cap. Near as I can tell a 1971 cap allowed for vacuum, but not vent...........How does a 1972 gas cap differ from a 71 cap?

Other than that I know the 1972 fuel sender and fuel pump have a return line, at least for a 402 with TH transmission. That's per the parts book. Perhaps AT transmissions are more prone to vapor lock.

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I originally planned to restore the fuel system to factory, but am entertaining the idea of a return line to avoid vapor lock. I'd rather not man what a PITA chasing down something nice that suits the current configuration along the frame rail, and perhaps another hole in floor.

How many of you have experienced vapor lock? My 72 350 Malibu did.
I never tried to figure that one out, got rid of it instead For what it's worth the truck will be running a factory 402 block and manifolds. The exhaust manifolds are being ceramic coated, which should reduce heat. Same with the stove & pipe. The rebuilt transmission may reduce heat as well with synthetic ATF.

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Interesting dispute over whether or not ethanol fuels contribute to vapor lock. https://forums.aaca.org/topic/279731...ives-or-ideas/


Here's some pics of a 70-71 EEC tank. Not sure if/how a 72 tank differs. Not sure what a 67-69 tank looks like either.

[71CHEVYSHORTBED402]

Interesting thread here. http://67-72chevytrucks.com/vboard/s...318544&page=32


I suspect 72 tanks were the same as 71?????? Still don't understand why a 71 gas cap differs from a 72.

On a side, to date I've yet to hear of a repop. vapor canister to suit. You'd think they'd be available, GM used mostly the same cans on 70-72............................Edit:, this link may clear that up some. He describes this beautiful cap as having a pressure relief valve. That doesn't sound like your everyday vent cap. Difference being a vent cap vents, while this cap blows when it has to..........Hmm........A provision where a vapor line fails? http://67-72chevytrucks.com/vboard/s...d.php?t=745146