What should i say, watch it how you put a new fuel filter on, fuel from your tank should drip in the OUTHER part of the filter (so dirt will be visible in time)
Itīs pretty normal that the filter sucs some air from the fuel-tap (especially when you leave the tap closed ;)
Even for non-injections machines it would be a wise decision, donī buy one tho from Kawasaki because they are very expensive. Better go to a car-parts shop.
if you have a carburettor system make sure the filter is big / has low resistance, because your engine could run lean if the filter doesnī flow fast enough (no pump to pull it through)
if somebody has some wise tips about this subject, write an article and mail it to me, i will make sure it is placed on the web.