I ran into this on Youtube and intuitively, it makes sense... but the know-nothing-newbie is known for his sophistical intuition, so I figured I'd submit it for your judgment:
It's an excellent idea, although obviously you should strip the carb apart first! Lemon juice is nothing more than weak citric acid and when heated does a great job of cleaning/dissolving gunk. Rinse in clear, hot water afterwards.
Let me put it this way.......after using the modern "politically correct" carb cleaners these days, this just HAS to be better!