In order to squeeze more horsepower out of current two-cycles, the design of piston rings has been steadily improved to contain combustion pressure more effectively. When too much carbon accumulates, the rings are pushed higher and higher. It's called ring jacking. Friction between the rings and cylinder walls increases considerably, elevating temperatures and accelerating wear. Eventually this causes very costly damage to the powerhead.
Most companies offer a separate carbon-reducing additive, too.
Don't Mix Water in gasoline is another serious problem. Moreover, the engine won't even run if there is too much water in the fuel system. While there are some additives on the market that use alcohol to absorb a small amount of water, the only sure way to get water out of a tank is to pump or siphon it out. Water, being heavier than oil or gasoline, will always go to the bottom of the tank. Once it has been completely removed, the rest of the fuel is fine.