Capped or Uncapped?

[FY1Cuda]

There's a very small tube sticking out under the choke housing on our Holley 4150.  What is it, and do we cap it or leave it open?

[HP_Cuda]

Cap it or you will have a vacuum leak, it looks like it's another external fitting for things like a vacuum line to the distrib.

Btw, what carb is that?

[roadman5312]

I believe its a vacuum line for choke pull off.  Vacuum advance is above it. 

[FY1Cuda]

Thanks. It's a Street Avenger 870.  I'll cap it.

[roadman5312]

Thanks. It's a Street Avenger 870.  I'll cap it.
[/quote
 Run a vacuum hose from it to the small tube under the front bowl. It operates the piston inside the choke housing.

[HP_Cuda]

Unless you don't care about the choke, then just cap it.

 

[FY1Cuda]

I'm no carb expert, but the choke is electric and has a coil inside that expands when given voltage, and that's what moves the choke.  I don't think there's any piston there.

[Fred]

Sorry for the hijack, but I have a new Holley with electric choke and that same red plastic piece behind it.  It often sticks and keeps engine idle too high.  I can move it with my finger and it unsticks to let engine slow down.  It will not move on its own, once stuck.  Am I missing something?

[roadman5312]

This is how it should be hooked up, the T can be eliminated.

[roadman5312]

The lever at top connected to rod that is connected to the piston. Vacuum pulls on the piston, causing choke pull off. It slightly opens the choke when engine starts.

[HP_Cuda]

That's a somewhat crazy design, so unless the car is idling the choke will go off.

I guess that will get around the waiting until the coil heats up via electricity trick, hence why many folks just disconnect them.

As for the red plastic piece, you can look here on how to setup your standard electric choke:
https://www.youtube.com/watch?v=0H5IBSFgYJE

[FY1Cuda]

Thanks, Roadman.  I didn't know there was a piston in there too.  It seems strange to me that the plumbing on the carb is such a mystery. I'd think that Holley would make it clear what you do with all the ports that come off it.  If those two are meant to be connected, why are they different diameters do you suppose?

[roadman5312]

Different diameters not sure. The port that comes from under the bowl is full manifold vacuum, so the unused end of the T can be used for trans vacuum modulator or vacuum to A/C controls. If not needed just cap off. Not for the vacuum advance,  , that is the tube above the idle mixture screw. Vacuum going to the piston will also influence how the fast idle cam operates. It can be very time consuming and frustrating to get the choke set just right so the motor fires right up.