The carb in your pictures looks like an offshore clone of the Ford Motorcraft carb that was used on various small block V8s. The vast majority of those things are worse than useless. It's way too big for a 250, so it will run rich because of the low manifold vacuum it creates. The power enrichment system will stay opened up all the time. Why not use the intake and exhaust the engine was designed for, instead of trying to outguess the entire GM research and development division? Putting headers on a 250 is like putting lipstick on a pig, unless you have done massive internal modifications to the engine and cylinder head to justify it, and plan to run full throttle and high RPM most of the time. Then adding twice as much carburetion as necessary just compounds the problem.
If you're going to insist on running non-stock intake and exhaust parts, let me suggest you try a Rochester 2 barrel for a late 1950s 265 Chevy V8, or a Stromberg 2 barrel for a 270 cubic inch MOPAR V8 from the mid-1950s. "Original equipment"- - -not something assembled by a 12 year old kid in a southeast Asia sweatshop. Either one will be much better than the carb you're running now.
Jerry
