OEM choke stove tubes were steel, used a woven fiberglass insulator sleeve, and were as short as possible to minimize heat loss. You probably need to lose the loop in the tubing and insulate it so enough heat makes it to the choke housing to be effective. That copper tube will dissipate a lot of heat in a hurry. If the fast idle linkage is adjusted properly, holding the gas pedal to the floor during a hot start will force the choke open. It's called a "choke unloader" and it's designed into the carburetor. No need to manually open the choke plate.
Jerry
