I've been using a homemade one for three or four years now, it works
well enough. I haven't seen one of the store-bought ones except in
catalogs. I did have to experiment quite a bit to find the right size for
the plate - ended up around 10 x 10 1/2 inches. I wouldn't be surprised
if you had to do a little trimming on one, especially with a 25 horse - I
would think you shouldn't be much too fast to begin with. Just curious,
is your motor a four stroke? I have one, and like it, but they have a reputation for not idling down as slow as a two cycle of the same size.