Wolfgang, the Shop Manual (p. 6-4) has a drawing of the Heat Riser Operation. When the flapper valve is in the closed position, routing exhasut gases up under the intake manifold, the counter weight is horizontal. As the spring heats, the counter weight drops toward the engine, going more vertical.

Doug

1947 2nd-Series GMC FC152 3/4-ton
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1953 Chevy Bel Air Sport Coupe Powerglide