I've hever had this problem in flying gas engines for about 10 years. Gasoline here in the USA doesn't have any additives that would "harden" and clog the carb. I'm quite at a loss to explain your problem, but I'll suggest the gas you're using may be impure and/or dirty. Be sure you filter the gas when filling your tank. I use two filters in the gas can supply line, and two in the line from the tank to the carb. If possible, do not use gas with ethanol or any other additives. Gasoline DOES get old and you should use only fresh gas. If you use the gas that's been sitting around in the can since your last flight, that may be part of your problem.

Good luck with it.

Dr.1