Sometimes the carb barrel screw on top of the carb sucks a little air. You may need to put some RTV silicone on it . Just make sure you clean the screw and tapped hole in the carb to get any oil or fuel off of them before you put the RTV on. The idle needle may also need this treatment. Once the RTV sets up on the idle needle threads, you can still adjust it. Just make sure to keep the RTV off the tip of the needle when you thread it back in. Check to make certain the carb barrel goes just PAST closed on the carb. If it's even a sliver open, it'll suck air. Try leaning the low end out as much as you can get it, but still maintaining a good transition.
Your front bearing is not sucking air...if it were, the engine wouldn't run at all. The rubber seal on that bearing is there only to protect the bearing from dust and dirt..nothing more. Hope this helps.