Vacuum Advance hookup - Firewall module?

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jarvitron

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Hello.

I tore all the accessories off my 318 (73 Dart) and while I was checking things out, I noticed that while my distributor's vacuum advance was hooked up (presumably to a properly sourced port on the carb), there was a plastic module marked "CARB" next to an two-vacuum port bit marked "Control Valve" on the far passenger side firewall. Pictures below.

What does this do, is it smog related? Can I safely leave it out of the circuit, or should I hook it all up again? What's the correct vacuum line configuration here?

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Is this an ac car? It could have something to do with vacuum actuators in the passenger compartment.
 
That is an OSAC valve. "Orifice Spark Advance Control". Nominally, its job is to delay vacuum to the vacuum advance, thus reducing NOx emissions from the engine and allowing the new 1973 models to squeak past their Federal emissions type approval tests so they could legally be sold. In fact, that's not actually how they worked. They actually worked by spoiling the driveability of the car: they created a hesitation/stumble so severe and dangerous, and took such a large bite out of acceleration at anything below full throttle, that you simply choose not to drive the car…thus reducing exhaust emissions!
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Leave it bypassed. Hose directly from the one and only correct nipple on the carburetor directly to the vacuum advance, without stopping anywhere on the way.

(Starting in 1974 the OSAC valve was moved to the air cleaner body)
 
Thanks! I figured as much but wanted to make sure I wasn't disabling something under the dash.
 
my 73 had those too,i made some blockoff plates for them.and kims right they induce a large stumble....
 
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