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Re: 66 c10 engine upgrades
The heat riser valve is controlled by a bi-metallic spring like an old school home thermostat. When cold it directs exhaust up under the carburetor to assist in keeping the mixture from condensing. As the engine warms up it opens and blocks exhaust from directly blowing on the bottom of the intake. The springs do corrode, the bushings and shafts wear, and it is possible for the butterfly to break free of the shaft and sit wherever it likes.
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