The heat riser valve is in the neck of the exhast manifold directly below the carburetor. Standing at the front of the car looking down at the heat riser, the weight will be rotated fully clockwise with the manifold cold. In this position it directs hot exhast gasses to the base of the curburetor. The weight should relax and rotate counterclockwise as the manifold warms up. Later models may not rotate until the engine is revved. That was a modification to improve fuel vaporization and lower emmissions. I believe the valves with a rectangular weight are the newer type; the older ones have a round weight. Someone else can probably add to ( or correct ) this information.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

The new ones are round. The weight is all the way clockwise untill the engine is started, snd then it is about half way (guessing) open. When the engine is revved, it opens more.

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'74 Duster 225 Super Six w/904
14" Cragar SS wheels