Why is a jet in 6G1 carburetor capped with a rubber plug?

[SteveVT]

Just a point of curiosity, the main jet in my '86 Mariner 8hp (Yamaha) 6G1 carburetor is what I would expect to see: a cast tube in the carb body with a brass jet orifice screwed into it at the bottom.

But next to it is another longer tube and brass jet orifice, and instead of being open to the fuel at the bottom, it is capped with a rubber plug. How does this jet get fuel?

Or is this just a storage place for an alternate or spare jet to replace the main jet if needed?

Pic of inside of a carb like mine --- rubber plug is the black piece next to the main jet.

 

[Faztbullet]

That is the idle jet passage and it gets fuel from main jet passage as its cross drilled.

 

[SteveVT]

Thanks fazbullet.