That's called a "heat riser", and it's pretty important for quick warmup. It should have a bimetal spring that holds it in the closed position when cold, and opens as the manifold heats up. It routes exhaust gas under the intake during warmup, and then drops to the full open position when the spring heats up. Use lots of penetrating oil, and work it through the full range of motion repeatedly until it works freely with no hangups. The butterfly is spot-welded to the shaft on assembly, so replacing one is a hassle. I have fabricated a new flap, and carefully welded it into place on some restoration jobs. Brazing won't work, because of the heat involved in that area. Kroil is the best penetratant I've found for freeing up a heat riser.

www.kanolabs.com
Jerry

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