Fuel & Emissions Hard Lines '72 A-body

Old April 10th, 2019, 08:45 PM
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Rodney
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Fuel & Emissions Hard Lines '72 A-body

I have a question about the emissions hard line that runs along the frame rail from the stand pipe (behind the rear seat) to the charcoal canister in the engine compartment. My car had only 2 hard lines running along the passenger side frame rail: a 3/8" fuel supply line and a 5/16" emissions vapor line. Both were badly rusted. When I ordered new lines, I mistakenly ordered a 1/4" fuel return line instead of the 5/16" emissions line. Would there be any issues with using the 1/4" line for the emission circuit or could this cause a restriction? It's only used for fuel vapors so using the 1/4" line might not be a problem and I'm not concerned with modifying the tubing.

Here's a pic:

The 1/4" hard line has the yellow cap, it needs to connect to the 5/16" line indicated by the red arrow.
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Old April 11th, 2019, 06:59 AM
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That'll work just fine, just make sure the hoses make a good seal onto that line.
Also make sure you have a sealed (not vented) fuel cap.
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Old April 11th, 2019, 09:50 AM
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Thanks!
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Old April 11th, 2019, 10:42 AM
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You realize the fuel lines only go to the frame section behind the front wheel, while the emission line is a much longer piece going to the canister.
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Old April 11th, 2019, 12:06 PM
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Rocketbrain:
I know the 1/4" line is shorter, but I don't see any problem with running a longer section of hose to canister. Thanks.
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Old April 11th, 2019, 05:35 PM
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Came up with another question about the vapor canister & emissions plumbing. The canister connected to the carburetor with a 1/4" vacuum hose. Was the port on the carb at manifold vacuum or was it a timed or ported vacuum port? I will be plumbing the canister to a FiTech EFI throttle body and not sure of the best place to connect. Thanks.

Rodney
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Old April 12th, 2019, 06:18 AM
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Originally Posted by Rocketbrian View Post
You realize the fuel lines only go to the frame section behind the front wheel, while the emission line is a much longer piece going to the canister.
Really? In my '72, even original, the vapor hard line ended pretty close to the fuel line. Maybe an extra foot?

Originally Posted by cdrod View Post
Came up with another question about the vapor canister & emissions plumbing. The canister connected to the carburetor with a 1/4" vacuum hose. Was the port on the carb at manifold vacuum or was it a timed or ported vacuum port? I will be plumbing the canister to a FiTech EFI throttle body and not sure of the best place to connect. Thanks.

Rodney
You want a metered port set up for ported vacuume. The metering is the hard part. I'm starting to cobble something together for my eventual EFI build using a late model solenoid that'll get triggered only when the engine is warm and cruising at part throttle so I can use a manifold port. My EFI throttle body doesn't have any ported connections.....
My current plan (not fully thought out, let alone tested) is to drill a hole, probably in the 0.060 to 0.080 range, in a plug and stuff that in the vacuum hose. I need to measure the hole in the qjet base plate....... Remind me - I've got one on the shelf, just need to actually do it.

The canister has little to no restriction, so it'll pass as much air as you please. Hence really don't want a wide open fitting.
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Old April 14th, 2019, 12:34 PM
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The stock 7042250 base plate has two holes for the canister purge, each approximately 0.050", located above the primary throttle blades. My "precision gauges" (aka drill bits) have a gap from 0.046 to 0.052, and the hole is difficult to get to without fully disassembling the base plate, so I'll say 0.050 +- 0.005.
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Old April 14th, 2019, 04:31 PM
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Oddball:
I'll be using a FITech EFI system. The throttle body has two 3/16" ports; one is timed (ported) and the other is full vacuum. I can use the full vacuum port for the distributor vacuum advance and the timed port for the vapor emission canister. Do you think the timed 3/16" port would cause a lean condition off-idle or should I plan to put a restriction in the 3/16" vacuum line as you suggested?
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Old April 15th, 2019, 02:36 PM
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Definitely put a restriction in it.
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