On top of the air filter case? It has been a while.

https://imgur.com/a/VFWKnp8

 

It routes fuel fumes to the charcoal canister on the underside of the air cleaner lid, so that they don't vent directly to atmosphere or migrate into the cabin. This is a 79/80 setup.

 

Thx

 

I much prefer this setup to the external canister, although it isn't as emissions friendly as the later setups. But what it does do is vent the carburetor bowls directly to the inside of the air cleaner, which is what you want for the carb to work properly.

And now I think I just stumbled upon why I had to rejet a 79 carb to run properly on my '81, when an '80 carb worked just fine on my '85. On my '85 I also used the '80 air cleaner setup, with my '81 I use the full '81 setup with the bowl vent going through the crankcase.

Hmm!! I have experiments to conduct!

 

Peejay, I just solved a hot start issue I had where the nikki would siphon fuel out of the bowls when parked hot and would be flooded and hard to start. Dumb me, I had plugged up the fuel vent hose barb on the carb. Once I vented that into the air cleaner, the problem disappeared.