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Hello everyone! I was trying to diagnose a rough running issue on my Packard, and when I was under the car I found a square lever thing on the exhaust manifold right under the intake. What is this lever thing? I tap it with my wrench, and it spins freely roughly 120 degrees.

Heat riser for the carb when cold. So you want that working. There should be a coil spring on that

Is the coil spring internal or external? There was no coil spring that I could see, and very little resistance. Could the heat riser cause issues when the engine is warm?

It's an external coil spring. It connects to the hear riser valve and holds it shut when closed. As it warms up it opens the valve and holds it open. Very easy to replace. Max Merritt has what you need.

-Kevin

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It’s flat bimetal thermostatic spring with the tab on the inside fitting into the slot in the shaft and the outer end is anchored by a pin on the manifold as shown in the illustration above. Be sure that the pin is intact and don’t run the engine much until it’s fixed and working as it blocks the exhaust.

Many folks pin or otherwise wire this open in lieu of the bimetal spring. You could do that while troubleshooting at a minimum. It slows warmup a bit but otherwise doesn’t affect operation. Mine was pinned open in my car long before I received it.

I think I'm just gonna pin it open. I live in Florida, so cold weather operation isn't really a major concern of mine. Thanks!

Good Morning...I live in Scottsdale, Arizona and all I did was remove the spring about 10 years ago and all has been fine. Ernie

I agree with you Ernie. My engine never had a spring, haven't had a problem with running or carb getting too hot. I am pretty sure the counterweight caused the flap to "fail-safe" in the open (warmed up) position. I don't want to pull my manifold off just to check this, can anyone confirm?
Gary

Yes, the counterweight on the heat riser valve holds it in the 'warm' position. This is a fail-safe so that the butterfly does not stay in the 'cold' position and allow the exhaust gases to rise continually as that would overheat the carb and possibly burn the valves. Drove my 261 Pontiac straight 6 for about 100,000 miles over 30 years with the heat riser valve rusted open with no issues. Winter and summer too, back when we had winter! No wire needed as gravity is your friend in this case!
Bob J.