Whats this piece

[littlebluedawg]

Wondering what this piece is and what needs to be hooked up to it. The truck had been running good but started a problem again. Seems like a vaccumm leak because the truck will idle good with the choke on and as soon as push the choke in, it wants to die. If i give it gas itll rev back up and then die. If i barely press the gas in, i can hear a hissing noise and itll die.

[geezer101]

That is a thermal vacuum switch. It's screwed into the base of the coolant journal and has no actual manifold vacuum in it. A vac hose goes in one way on a barb and then goes back out to whatever control circuit it's connected to. If you've got a vacuum leak it'll be somewhere else.

[camoit]

Yeah that sounds like a lean condition. Could be vacuum leak or the MCA jet valves.

[littlebluedawg]

Ok, thanks. I turned the idler screw in on the carb and that helped a lot. Ill chase it down eventually