You are not using enough heat!

Once you have the airhorn (potmetal), bowl cover (potmetal), and the float removed from the carburetor; you can use an acetylene torch, and heat the CAST IRON AROUND THE PLUG until it is cherry-red. DO NOT QUENCH IN WATER!!!!! While still hot, carefully so as not to burn your selfself, unscrew the plugs.

All parts are available for that carburetor, including the plugs.

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