Hi folks, could anyone tell me what the small rubber pipe coming out from my metering head is for? It's about 10mm dia and 6" long with several blue clips. It's located just under the air flap on the left hand side.

I removed my cylinder head for machining and can't remember if I touched it on reassembly. There's nothing obvious that it attaches to. I'm concerned I've missed something. I'm jot at the stage to start the car just yet.