I would like to know how #9 works. I can understand the idea of 3 ports- an in port, an out port, and a vacuum port to open and close it. Why does this one have 4. I can't quite figure out the flow of fuel vapor. I know it enters the large bottom port and I thought it could only exit through the the big port just above it. Yet diagram looks like fuel vapor could go up to top of valve. I'm confused, and would like to understand this valve and how it interacts with the carb. thanks. This is on a 84 z28 305. I just noticed that this diagram is missing the tank pressure control valve that should be on line #8

 

It collects vapors from both the fuel bowl and the gas tank when the engine isn't running.

The pressure valve isn't in Line #8. It has its own port off the tank pick-up.

 

I think this is starting to make sense now. All fuel vapors are drawn back into the carb or actually the throttle body by port #3. Both bottom ports, 4 & 10 are actually in ports. Correct??

 

Wait, I see what you mean by the control valve. Never mind what I said.

https://www.thirdgen.org/forums/atta...se-routing.jpg

The tank and fuel bowl are open to the canister when the engine isn't running. When running, the vapors are pulled out of the charcoal bed into the engine by the flow of fresh air from the bottom of the canister.