On my 69 Camaro 6 cyl, there is a metal line that comes up from under the firewall, above the trans, and goes to the carb. Near it on the base of the carb is a vacuum fitting. Do these get connected together? With vacuum hose ? What does this line do ?

If the trans is an automatic, engine vacuum is use to make it shift.The line could be the one that goes to the transmition.

If the trans is an automatic, engine vacuum is use to make it shift.The line could be the one that goes to the transmission.

It's the vacuum line from the base of the carburetor to the modulator on the left side of the transmission; the modulator controls transmission shift points based on engine load. Make sure it's properly connected at both ends with no leaks or it won't shift properly. There's another vacuum port slightly higher on the carburetor, but that's for the distributor vacuum advance.

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JohnZ
'69 Z28 Fathom Green