Britt giving dizzy advice...
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Anywho...
The one vacuum line you have on your TB on the 74 2.0 is for the retard on the dizzy. The 73 2.0 TB had both advance and retard ports, but they changed the TB in 74 to retard only (for emissions), but contimued to use the same dizzy. Hence, the two ports on the dizzy but only one on the TB for the 74 2.0. Generally speaking, and is the case with a 914, a vacuum port on the can of the dizzy is advance and the port on the 'back' side of the dizzy is retard.
You need to disconnect and plug the vacuum hose, time the motor, and then reconnect the vacuum hose from the TB to the retard port on the dizzy.