Well here is my two cents worth, yes the water sprayed into the carb, in small amounts, will in some cases dislodge carbon build up on the tops of the pistons. The theory is that the cold water hitting the hot carbon will cause it to loosen and burn away. There are numerous products sold that are supposed to do the same thing when poured down the carb. They also are good mosquito foggers as they produce huge amounts of smoke out the exhaust. As for the spark plug electrode, I have done this on my sons racing go-kart years ago, used a Volkswagen plug in 5hp Briggs and sawed half the electrode off, this gives a better flame pattern in the cyl. It did improve performance somewhat, but we also were running alcohol fuel. The split fire plugs sold now are based on the same principal. Funny how a lot of things we old backyard mechanics came up with worked fairly well and were commercialized.