Did you change ANYTHING else besides the fuel line? Did the carburetor move when you were installing it? How was the carb sealed to the manifold before you changed the fuel line. If you read the lable you'll find that most RTV, silicone based products are not compatible with gasoline. Gas will eventually eat them and then you have an air leak where the carburetor attaches to the intake manifold. Look for a product that is gasoline compatible such as SealAll, available at most auto parts stores. As GoatHerder said, your symptoms are those of an air leak in the intake system. Also make sure the carb slide (barrel) is moving smoothly and fully returning to the idle position when you release the twist grip. Kinks in the throttle cable can cause the slide to stick also.
Tom