Re: Straight eight manifold flapper

Posted by HH56 On 2019/7/28 16:43:28

It is called the heat riser valve. If the valve is stuck closed it can result in overheating and also valve burning.

Purpose is to help warmup in cold climates. There is a thermostatic spring that when cold increases tension and moves the valve to the closed position. This forces some exhaust to pass thru an auxiliary passage in the manifold and up toward the carb to warm the base and surrounding area so the gasoline can vaporize a bit easier. As the engine warms, the thermostatic spring is also warmed and loses tension. That action lets the weight pull the valve open to close off the aux passage and allow the exhaust to go thru the normal route to the tailpipe.

In moderate or temperate climates some feel it is not that important. If you live in a temperate area and the spring is missing or the valve shaft is rusted and sticking you can make sure the valve is open and then wire it so it stays open. Once you are sure the valve stays open you can add to the list and repair as needed..