Where does this hose go ?
Thread Starter
Instructor
Joined: Apr 2016
Posts: 207
Likes: 31
From: Fishers Indiana
Where does this hose go ?
Found a new loose hose along with some soot beneath my 74 convertible today. See pic attached. Is this canister beneath the washer reservoir the charcoal canister? I looked in my aim manua but the canister page was so hard to read to not be of help. The loose hose connects to the port on the right (when looking at it from passenger fender). Where does the other end go ?
Thread Starter
Instructor
Joined: Apr 2016
Posts: 207
Likes: 31
From: Fishers Indiana
Le Mans Master
Joined: Aug 2006
Posts: 7,419
Likes: 1,555
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Hello OO7,
If your 74 is like mine then you only have two ports on the vapor canister.
One line connects to a 'ported vacuum' port on the carb.
The other line attaches to a hard line and goes towards the tank.
If your 74 is like mine then you only have two ports on the vapor canister.
One line connects to a 'ported vacuum' port on the carb.
The other line attaches to a hard line and goes towards the tank.
Thread Starter
Instructor
Joined: Apr 2016
Posts: 207
Likes: 31
From: Fishers Indiana
Thanks Peterbuilt - my AIM manua page looks same as what you posted but i cant make any of that out.
So i recently had he carb rebuilt, and a full tune. I dont see any open ports on the Rochester carb. Im wondering now if this canister outlet port has been disconnected for awhile and i just failed to notice. The fuel tank line is hooked up fine. What repercussions are there by not connecting the canister to the carb ? Can i leave it alone ?
So i recently had he carb rebuilt, and a full tune. I dont see any open ports on the Rochester carb. Im wondering now if this canister outlet port has been disconnected for awhile and i just failed to notice. The fuel tank line is hooked up fine. What repercussions are there by not connecting the canister to the carb ? Can i leave it alone ?
Team Owner
Joined: Sep 2006
Posts: 31,200
Likes: 4,287
From: Westminster Maryland
Hi V,
The purpose of the charcoal in the canister is to 'capture' and hold the gasoline vapors while the engine isn't running.
Once the engine is started the gasoline vapors are 'pulled' from the charcoal by the engine's vacuum.
If the hose from the canister to the engine isn't in place the charcoal in the canister can become saturated with gasoline.
At first this can be sensed by a gasoline smell in the garage or as it becomes more saturated a drip from the bottom of the canister.
Regards,
Alan
The purpose of the charcoal in the canister is to 'capture' and hold the gasoline vapors while the engine isn't running.
Once the engine is started the gasoline vapors are 'pulled' from the charcoal by the engine's vacuum.
If the hose from the canister to the engine isn't in place the charcoal in the canister can become saturated with gasoline.
At first this can be sensed by a gasoline smell in the garage or as it becomes more saturated a drip from the bottom of the canister.
Regards,
Alan
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Thread Starter
Instructor
Joined: Apr 2016
Posts: 207
Likes: 31
From: Fishers Indiana
Thanks Alan- very helpful explanation. So it appears i need to find which port on the carb this line needs to run to. The aim manual is hard to read in this sense to show me the carb port in detail. Any guidance on a schematic or pic that might better show where the canister is supposed to connect in this standard rochester carb ?
Hi V,
The purpose of the charcoal in the canister is to 'capture' and hold the gasoline vapors while the engine isn't running.
Once the engine is started the gasoline vapors are 'pulled' from the charcoal by the engine's vacuum.
If the hose from the canister to the engine isn't in place the charcoal in the canister can become saturated with gasoline.
At first this can be sensed by a gasoline smell in the garage or as it becomes more saturated a drip from the bottom of the canister.
Regards,
Alan
The purpose of the charcoal in the canister is to 'capture' and hold the gasoline vapors while the engine isn't running.
Once the engine is started the gasoline vapors are 'pulled' from the charcoal by the engine's vacuum.
If the hose from the canister to the engine isn't in place the charcoal in the canister can become saturated with gasoline.
At first this can be sensed by a gasoline smell in the garage or as it becomes more saturated a drip from the bottom of the canister.
Regards,
Alan
Le Mans Master
Joined: Aug 2006
Posts: 7,419
Likes: 1,555
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
There are several ports on your carb.
To tell which port is which use a vacuum gauge.
MANIFOLD vacuum ports have vacuum at idle and above idle at any steady RPM..
PORTED vacuum ports have no vacuum at idle but do have vacuum at higher steady RPM.
EX: Your PCV valve is on a ported port.
To tell which port is which use a vacuum gauge.
MANIFOLD vacuum ports have vacuum at idle and above idle at any steady RPM..
PORTED vacuum ports have no vacuum at idle but do have vacuum at higher steady RPM.
EX: Your PCV valve is on a ported port.
Thread Starter
Instructor
Joined: Apr 2016
Posts: 207
Likes: 31
From: Fishers Indiana
Roger that Peterbuilt and thank you
One last concern - lets assume my recent tune/carb rebuild was done without the canister plugged into a ported vacuum port. When i go plug this in now, would you expect my tune to be off ? This is new load on the carb that wasnt there before. Or am i overthinking this?
One last concern - lets assume my recent tune/carb rebuild was done without the canister plugged into a ported vacuum port. When i go plug this in now, would you expect my tune to be off ? This is new load on the carb that wasnt there before. Or am i overthinking this?
There are several ports on your carb.
To tell which port is which use a vacuum gauge.
MANIFOLD vacuum ports have vacuum at idle and above idle at any steady RPM..
PORTED vacuum ports have no vacuum at idle but do have vacuum at higher steady RPM.
EX: Your PCV valve is on a ported port.
To tell which port is which use a vacuum gauge.
MANIFOLD vacuum ports have vacuum at idle and above idle at any steady RPM..
PORTED vacuum ports have no vacuum at idle but do have vacuum at higher steady RPM.
EX: Your PCV valve is on a ported port.
Le Mans Master
Joined: Aug 2006
Posts: 7,419
Likes: 1,555
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Just hook it up!
It will not affect your tune up.
You will have to decide if you want ported or manifold vacuum to your distributor.
See Lars posts here:
https://www.corvetteforum.com/forums...cuum-port.html
You will have to decide if you want ported or manifold vacuum to your distributor.
See Lars posts here:
https://www.corvetteforum.com/forums...cuum-port.html
Tech Contributor
Joined: Aug 1999
Posts: 14,373
Likes: 6,371
From: At my Bar drinking and wrenching in Lafayette Colorado
There are several ports on your carb.
To tell which port is which use a vacuum gauge.
MANIFOLD vacuum ports have vacuum at idle and above idle at any steady RPM..
PORTED vacuum ports have no vacuum at idle but do have vacuum at higher steady RPM.
EX: Your PCV valve is on a ported port.
To tell which port is which use a vacuum gauge.
MANIFOLD vacuum ports have vacuum at idle and above idle at any steady RPM..
PORTED vacuum ports have no vacuum at idle but do have vacuum at higher steady RPM.
EX: Your PCV valve is on a ported port.
Lars
Le Mans Master
Joined: Aug 2006
Posts: 7,419
Likes: 1,555
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Thread Starter
Instructor
Joined: Apr 2016
Posts: 207
Likes: 31
From: Fishers Indiana
Just to close this thread out - upon inspection the port next to the idle screw on my carb was capped. Not sure if that happened before or during the carb rebuild but the cable was surely there before given hose length and your guidance. Car continues to idle fine as you said it would. Thanks All