Mody, did you buy this engine used??? The O-ring under the carb is there for a good reason and if you don't have one then it can cause a lot of different problems. When I buy a new engine the carb is usually not installed. The carb and O-ring need to be installed by the owner. You install the O-ring on the carb then push and hold the carb down with pressure and tighten the carb down with the screw. This stops air leaks. If you buy fuel in cans and keep it in a cool DRY place it doesn't go bad with age. You can keep it around for decades and it will still work. If you buy it in plastic jugs and keep it in a cool dry place out of the sun it will out last the plastic jugs. Loose caps in humid areas can allow moisture/water to get into your fuel and then it is no longer any good. If the cap is tight on your can it will last for decades. There are right ways and wrong ways to store your fuel, done correctly your fuel is never a problem, done wrong and you will be wondering why the new engine isn't running.