The flap should close when the engine is cooling off. On a cold start, check to see where the flap is and if you can move it one way or the other. This flap directs exhaust up and around the base of the carburetor through casting holes in the intake. As the manifolds heat up, the spring relaxes letting the weight on the flap arm pull the flap closed. This then directs the exhaust out the manifold and down the pipe. In your climate, intake manifold heat is very important.
Keep monkeying with the linkage, if you go to far, the engine will let you know.
