nope...most definitely not.... there is no seal in the bearing and the fuel will not harm the bearing no matter how rich you run the engine. in fact the more lubrication you give the bearing the happier it is.........believe it or not but the fuel itself is what seals these engines....

Now if the engine is crazy rich it can pump fuel out the front bearing which can cause dirt to collect, and if you then run the engine really lean afterwards that dirt may get sucked in....but the engine being pig rich and pissing fuel out the bearing will do no harm to the bearing at all....