Identify this please!

mercredi 31 août 2016

Hi everyone, new to the triangle engine. Bought a '04 with the engine out of it, but new rebuild. I have the engine in, hooked up, fluids in, it starts, but only runs for a couple seconds. I found this open nozzle above header on passenger side. What is it? How do I hook it up/where does it go to? Thanks :)