Jerry is correct about the steel choke tube (tubing insulation used to be available from NAPA, have not tried recently).

The choke should NOT close immediately, regardless of the material used for the tube. Check that the fast idle linkage is correctly adjusted.

Jon

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop