Big Block Fuel Lines - Team Camaro Tech
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post #1 of 12 (permalink) Old Feb 12th, 01, 11:12 PM Thread Starter
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Not sure if this is the right forum, but....
I understand that factory 396's came with two fuel lines. Mine was retrofitted and I only have one.
What was the purpose of the second line? Was it a fuel return from the pump, like fuel injected cars have?
Is there a reason for me to change anything? It runs fine now.
Thanks for the help.
Joe


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post #2 of 12 (permalink) Old Feb 13th, 01, 12:16 PM
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I believe the 2nd fuel line was an overflow return line from the carb? Just depends on the carb you are using, but chances are you don't need it. Someone correct me if I'm wrong......KZ
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post #3 of 12 (permalink) Old Feb 13th, 01, 02:13 PM
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The second fuel line is a return line from the fuel filter to the tank on 325/350 HP 396s. One reason for the large filter is to act as a fuel reservoir for sudden acceleration under load, like climing a hill. It is possible to run a QJ dry in these rare instances and the filter prevents that. You may never notice a difference.

If there was no return line the filter would burst.
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post #4 of 12 (permalink) Old Feb 13th, 01, 02:23 PM
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William is correct. This also applied to the 69 SS-350/300hp. Same setup.
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post #5 of 12 (permalink) Old Feb 13th, 01, 11:49 PM Thread Starter
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I'm running a Holley 750 DP; haven't had any issues with it running dry!
Now if I could get it to run a little leaner, maybe I'd get 6 mpg instead of 5!
Thanks
Joe

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post #6 of 12 (permalink) Old Feb 14th, 01, 04:43 PM
kel
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I believe the double fuel lines were on the 1969 first gens only.

My 1968 does not have the double fuel line and it is an orginal BB car.

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post #7 of 12 (permalink) Old Feb 16th, 01, 12:44 AM Thread Starter
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Thanks, guys. I guess I worry/wonder needlessly! But that's how we learn!
Joe

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post #8 of 12 (permalink) Old Feb 16th, 01, 03:05 PM
 
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The dual fuel lines were for the low performance BB's and the SS350 that were equipped w/quadrajest's. The hipo cars, Z-28, COPO, 397-375 hp had a single 3/8" line.
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post #9 of 12 (permalink) Old Feb 16th, 01, 05:41 PM
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The second fuel line was a return line to prevent vaperlock. It was used mostly in air conditioned cars. All big blocks came with a 3/8 fuel line On some cars the fuel pump itself had a return port in it. I don't know where the big filter helping a Q jet not run out of fuel came from but don't believe it. A holley is far more prone to fuel problems in straight ahead excelleration.

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post #10 of 12 (permalink) Old Feb 16th, 01, 11:17 PM Thread Starter
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Thanks, guys!
Joe

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post #11 of 12 (permalink) Old Feb 17th, 01, 10:59 AM
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The fuel filter w/return line has nothing to do with vapor lock or A/C. All 1969 300/350, 325-350/396 cars were built that way A/C or not. Vapor lock is caused by fuel percolation in the carburetor. QJs used a steel gasket under the carb to insulate it from engine heat. Another fuel line 6" from the carb will have no effect.

Whem Holleys run dry it is mostly a fuel pump volume problem.
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post #12 of 12 (permalink) Old Feb 17th, 01, 12:22 PM
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Vapor lock is the fuel turning to a gas in the fuel line not the carb once it gets to the carb it will either go out the vent or into the vapor canister if so equipped. The reason for the stainless plate under the
Q jets is the exhaust crossover is open under the carb and it will destroy the Q jet base very quickly.

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