Yes, the stock manifold is heated by the exhaust manifold and heat is regulated by the flap and bi-metal spring. You should make certain yours is working correctly. The bi-metal spring for the 235 is rather expensive, but seems I saw where somebody was using one made for a Jeep which was much less costly and worked the same.
The Carter (at least in my experience) is more smooth running and consistent than the Rochester. A large part of the problem with any Rochester B or BC carburetor is the power circuit. There's a power piston in there which is controlled by manifold vacuum which passes up from the throttle body and from there through the float bowl and from there to the air horn where it sucks the power piston up off the valve ball. If this doesn't happen (which is common due to either a loss of vacuum from a warped carburetor casting or simply a stuck piston from ethanol-laced fuel), the carburetor will run as rich as it possibly can all the time you're driving. In this condition, your gas mileage will probably be in the single digits. The whole scheme with that circuit is that when the engine loses vacuum (in the case of greater demands on the engine from hills, acceleration, etc) the power piston will be forced down by the spring which controls it. Then when this happens, the power valve will open up and flood the mast with more fuel...a lot more. There's a restrictor in there, but it doesn't really restrict much. The carb will still run as rich as Croesus. In the days when the carburetors were new and we had real gasoline, these carburetors worked better. But today problems are not easy to avoid and the Rochester design was never heralded as a stroke of genius. If you see one leaking at the float bowl to air horn gasket, the casting is warped and/or somebody forgot to put a gasket between them. Last summer I spent a lot of time and effort showing what this warpage was and how it can be corrected rather simply with a piece of 3/8 inch thick steel, common bolts and nuts, a dial gauge, some patience and common sense and a gas grill. All that work is posted on this site. But I'm told by learned men that even if you correct it, the same situation will return in a few years.
The Carter design doesn't have this power circuit...it compensates for extra power needs in other and saner, more logical ways. I've never been a fan of trying to adapt 2 barrels or 4 barrels to a 235. Even though I've always liked the 235 a lot, it is a dandied up tractor engine and over-carbureting it isn't necessary or even wise in most cases.
