Double barrel is a good upgrade, easy to install and more out there. Could have had a fully working 318 engine in there for 200$ more. Anyways, as every one else said here, fix that choke. Hey, put in a manual if need be, they sell at canadian tire for cheap and you will never have vacuum, thermostatic, heat riser, etc choke problems again. But getting back to it, if that choke is ok, you have to know if that float is level, power pump is working, linkages not binding and not bent, a good sign is at rest the rods should all be loose and not forcing one another. Is the base gasket sound and not pulling air. Ain't gonna get no power if choke plate is closed after start up and warm up. Is the throttle shaft binding? Usually a carburator is pretty simple and doesn't lack power unless something else is affecting it, it may be hard to start, may stumble on acceleration due to a bad power pump, other issues causing poor power are fuel pump not delivering at high rpm. worn cam lobe or bad diagphram(sh%t can't spell that word). Bad EGR vavle?