1971 250C Exhaust Dampers?
 

The above car runs well around town with its original twin zenith carbs, but boggs down at highway speed. Rather than mess with further carb adjustments, rebuilds, etc, I bit the bullet & bought JAM Engineering's Weber carb kit.

Upon removing the Zeniths, I noticed two "dampers" on each of the ports in the exhaust manifold. It appears the dampers are supposed to be opened by bi-metalic coils as the engine warms.

Both coils are broken & it appears the forward damper is seized in the open position, while the aft one moves freely & may have been open and/or closed as I drove.

Dos anyone have experience with these things & how they affect performance?

That's a common problem on these cars. Check out this link.

http://www.peachparts.com/shopforum/vintage-mercedes/237863-1967-250s-exhaust-flaps-frozen.html

On mine, I ended up getting a piece of steel to close off the heat risers.

Alternatively, post #6.

http://www.peachparts.com/shopforum/vintage-mercedes/238292-m115-t-b-i-conversion.html

Thanks, fellas. I'll leave the forward heat riser sealed shut (San Francisco) & secure the aft in the same position.
Regards, C