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2 hoses come from the charcoal canister on a 71, one goes to the pcv valve, the smaller one goes to the carb, my question is should the carb hose (smaller one) go to a ported or full time vacumm source? I have been told that it should go to a ported source, I do not have an original carb, so the assembly manual does not help. What is this vacumm source acomplishing??
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Re: charcoal canister vacumm hose routing c3
There should actually be four hoses at the cannister. One is from the fuel tank vent and one from a carb bowl vent.
The other two are the cannister purge signal line and cannister purge line. The cannister purge signal line should be connected to a ported vacuum source, and it is the smaller of the two hoses. It attaches to a nipple on the purge valve cap at the cannister.
The larger purge line hose connects to a nipple on the neck below the purge valve cap.
The nipples are marked "carb" and "pcv", respectively, on the cannister.
The way it works: If the throttle is open enough to provide a vacuum signal to open the purge valve, manifold vacuum draws a metered amount of air through the cannister to purge the activated charcoal of trapped fuel vapors.
All of the above should be explained in your Chassis Service Manual.
Duke -
Re: charcoal canister vacumm hose routing c3
Duke, you are the man. I have a similiar question. I get a noticeable gas smell
when I park my car back in the garage. It takes some time for the smell to
finally calm down. Is this a canister build up problem. Mine is the original
1972 never been touched. Or is the smell coming from the carb. Carb was rebuilt
about 2 years ago, it is also the original carb, was rebuilt once before that
in about 1978.Comment
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Re: charcoal canister vacumm hose routing c3
I had a similar problem on my Cosworth Vega a few years ago, and what I found may give you a hint where to look.
...strong fuel odor in the garage. The CV has two steel pipes from the fuel tank vent to the cannister. One routes from the tank to the cowl and the other from the cowl to the cannister, which is behind the LF headlight housing. There is a short piece of rubber fuel hose connecting the two pipes at the cowl and the front pipe to the cannister (in addition to a third short hose from the rear pipe to the tank vent nipple).
The hose connecting the two pipes at the cowl is behind the engine right where the cowl turns back to the transmission tunnel and not easy to access, but I finally found that this hose was split at one of the spring clamp connections. Being close to the engine probably helped degrade it over time from the heat.
So the message is to check all the hoses and connections. Also verify that routing of all the various hoses is IAW your CSM.
Evaporative system rubber hoses are the same as conventional low pressure fuel hose used for carbureted engines - SAE 30R7.
DukeComment
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PS
It might be a good idea to pop off the purge valve cap (slowly so the spring doesn't fly away) and check it for cleanliness and proper function. Also check the filter on the bottom of the cannister. It's a white woven fiber type material.
The filter can actually be washed in soap and water, but I purchased a Purolator replacement at Pep Boys for about a buck and a half a few years ago. It looks just like OE, and GM build millions of these cannisters in that era that were essentially all the same on all cars and light trucks.
The "carb" nipple on the CV's cannister has a cap on it because the EFI fuel rail is sealed with no vent. The throttle body has a ported vacuum nipple for the purge signal line and a full manifold vacuum nipple for the purge line.
DukeComment
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