Turn the switch on the crock pot to low not high. I have been told that high will discolor the aluminum. The anti-freeze will not hurt the rubber hoses of a car so you could probably soak the complete engine. I have never put a carb in to soak just all the rest of the parts, some of the crud off the engine could wind up somewhere in the carb. Some of the thickest burnt on crud had to be scrubbed with a tooth brush or wooden popsicle stick.
Do this out in the garage with plenty of ventilation, the fumes can't do you any good. The anti-freeze can be used over and over. I have done many engines for friends and they have all turned out sparkling clean.
FB