Quote:
Originally Posted by gmtech68
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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I'm pretty sure mine is days away from getting ejected from the tailpipe. Whenever I start the truck there is an awful rattle for the first 30 seconds that sounds like a putty knife in a fan.