39 Chrysler manifold heat riser

[Brooklyn Beer]

Mine is missing the spring and none functioning and just flops back and forth.  Until I can find the spring what is the correct position of it closed to stop heat transfer for the summer?  Lever up or lever down ?  With good gas today I doubt I even need it

[keithb7]

I had one apart recently. All the way clockwise till it stops, closes the valve so no heat transfers up to the carb base.  The one I was inspecting was from 1949. 

[Brooklyn Beer]

Thank you.  Mine seems to be almost weighted to go in that direction.  Will put a simple spring to it.

[jpage]

Any spring will not work. The coil spring is heat sensitive. As the engine gets hot the spring loses tension allowing the weight to open the valve. All of the Mopar parts suppliers should carry correct springs.

[Fossil]

13 hours ago, jpage said:

As the engine gets hot the spring loses tension allowing the weight to open the valve.

Do you mean it opens to let all the exhaust go straight out the header pipe? 

[Brooklyn Beer]

I would say so being the car only needs heat for the cheap fuel at start up to help atomize.  Fuel back then was not a good constant. It was so bad back in 30-31 that Franklin actually had what can be described as a toaster element in the fuel supply to create gasoline vapors on cold starts. Imagine putting a red hot element much like a cigar lighter into today's gas.

[keithb7]

It is my understanding that when fuel is vaporized inside the carb venturi, it looks like a fog. When this fog touches cold steel it condenses back into tiny droplets. They form on the insidewalls of the intake manifold. Imagine a cold beer on a hot humid day. Humid air condenses on the beer bottle and forms water droplets.  

A cold engine runs rough. Fuel is not delivered evenly to all cylinders. As the exhaust gasses exit the cylinders, the hot gasses are re-directed up to a special area up under the carb. It warms up the carb base and intake manifold quickly.   The exhaust manifold valve that performs this task is shown in my pic above.  It is indeed controlled by a bimetallic spring and a counterweight. As the valve spring gets hot from exhaust gasses, it expands and spring tension becomes weak. The Counterweight overcomes the spring. The valve closes and no more hot air is is directed up to the carb base.  The intake manifold is warm now. Fuel is atomized well and evenly delivered to all cylinders.
 

The Carb auto choke works similarly. A choke is closed to allow less air into the carb, to create a rich A/F mixture. The engine needs extra fuel, at least partially due to reasons mentioned  above. 
 

The warm engine runs smooth and even. The choke and exhaust manifold valve are now backed off automatically by the exhaust heat, having little to no effect at this point. 

Edited June 1, 2020 by keithb7 (see edit history)