I could use a 1974 slant six manifold heat control valve expert!

slantsixdan said
"Boomy" sounds like you've got a big exhaust leak. Which gaskets (brand) did you use when assembling and installing the manifolds?

Ceramic coating on the spring is not good. That's a bimetallic strip wound into a spiral. It wants to be naked metal in order to function properly.

With the engine cold, grasp the counterweight and rotate it anticlockwise (as viewed from the front). It should turn easily, but there should be noticeable spring tension. When you let go, it should promptly spring back clockwise until it hits a hard stop. The total amount of rotation from one extreme to the other is roughly 90°.

With the engine hot, do not grasp the counterweight without a heatproof glove or something, or you'll burn yourself. But everything should work the same as described for a cold engine, except the spring tension should be less.

That valve is there for a good reason and unless you're building a race car, removing/defeating it is all drawback, no benefit.

Dan, thanks for your reply. We used Fel-Pro gaskets. I cannot detect any exhaust leaks in any of the three exhaust manifold gaskets. I'm puzzled by the end of the spring dangling free when the engine is hot. You can see that in the first photo. To me, the spring end should still be in contact with the peg, but it isn't when the engine is hot. Then I just noticed something from the FSM. I'm attaching a photo of this valve from my shop manual. Notice how the bent end of the spring rests against the left side of the peg in the FSM photo. On my car, the bent end of the spring is to the right of the peg. Does something look wrong to you when comparing the photo of my spring to the photo from the FSM? To me, it almost looks like the thermostatic spring is on the shaft backwards. The funny thing is that it was running fine (no "boomy" sound) before we removed and ceramic coated it. If it is backwards, how hard is it to turn the spring around? The part number on my manifold is 3671862, and is dated J-17 73. The factory parts manual says the exhaust manifold should be part number 3744827. I'm puzzled by this whole thing. Your thoughts?