Throttle body cleaner not carb cleaner will do it instantly with no scrubbing. It dries fast though so if the liquid gets around the pistons and int the rings, it may transfer the carbon into the rings and harden around them. It leaves a carbon "sap" behind if you don't wipe it up while it is wet.
It works great for throttle bodies, but maybe it isnt so good for pistons while they are in the engine. I used a metal scraper, and a bunch of cleaners, I just use the throttle body cleaner in the intake manifold. Amazing stuff, though.

Sold Truck: 89 DLX extra cab 4x4 22re Automatic/ New truck 97 T100 4x4 auto Sr5