We run on Mercury Outboards!
A fly line gets dirty like anything else, and should be cleaned every few trips. RIO's Wonder Cloth from RIO Fly Lines is a micro abrasive cleaning pad that strips out the deep-lying dirt without roughing the fly line. For best results finish by applying a coating of Agent X fly line dressing.
There are 4 of the 3" x 5" Wonder Cloths in each pack.