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The ‘why’ of the manifold drain is a good question, Randy…
…a possible explanation is that as crankcase ventilation is directed to the throttle body - to be sucked, via the manifold, to be burnt in the engine. Residual oil will condense in the manifold over time, and drained out through the vent while the engine is standing. As will residual petrol in the manifold - whether from carbs or fuel injection.
However, the vent is a ‘vacuum leak’ when uncapped, but that is easily compensated by other adjustments, like the mixture screw…
No serious issues has been brought forward with the drain capped or uncapped…?
Frank
xj6 85 Sov Europe (UK/NZ)
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