Quadrajet with no charcoal canister vent...

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MrSony

Geezer
Nov 15, 2014
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Des Moines, Iowa
what do I do when my carb doesn't have the big 3/8 nipple on the front? How did the earlier cars run the emissions hoses?
 
This isn't me [hopefully Tyler won't mind] but he has the basic idea . . . should be useful. If I am misunderstanding your question, repost, I'll try to help or confuse you more 👍.

 
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The carb I'm looking at for a replacement has no hole for the vent tube in the body. I wonder if the passage would still be in there so I could just drill and add the tube.
 
Just leave it open at the canister so the fuel tank can vent. The whole idea of that port is so as gas is pumped out of the tank it needs to draw in air, so by drawing it through the vent in the carb fuel vapors will be drawn back into the tank instead of gioing into the atmosphere. Earlier cars didn't have this, they just vented into the air.
 
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If you want to add the vent tube you need to take off the horn to make sure the port and channel are there in the older style carbs. The circled port in the body lines up with the channel in the horn for the bowl vent tube..

carb 1.jpg
carb 2.jpg
 
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How old is that carb? They used to have a vent on the top of the air horn with a spring loaded rubber disc. At rest it closed the hole and at any throttle opening it opened. The hole was closed up approaching emissions carbs but you still saw the castings for the spring and plug mechanism. I forget what year it happened but the vent tube was added to the carb, the tank had a non-vented gas cap, and the charcoal canister appeared.
 
And you have to be a little careful on leaving open ports on that canister. It is amazing how much vapor that thing will absorb. When I moved it from PS to DS over my dual CAI mod, I thought I knocked or cracked something loose in the gas line. Started smelling gas. Nope, just that canister.
 
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Just leave it open at the canister so the fuel tank can vent. The whole idea of that port is so as gas is pumped out of the tank it needs to draw in air, so by drawing it through the vent in the carb fuel vapors will be drawn back into the tank instead of gioing into the atmosphere. Earlier cars didn't have this, they just vented into the air.
And the cars smelled like gas.
 
And the cars smelled like gas.

I would think you may have some other issue, maybe a bad line or the canister itself has a crack. The system should be drawing in air via the canister as fuel is used. I've done this to several cars over the years and never had that issue. On one car, i capped the canister and actually built up a vacuum in the tank to the point that when i went to gas up, the tank poped out with a loud noise. The other way you could go is to plug the canister and get a vented gas cap like older cars had or modify the one you have.
 
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