1985 suzuki dt140 not charging battery

well... been stuck with this motor for a while, trying to put as little money as possible into it. It runs pretty good, but doesn't charge a battery. I have replaced the rectifier, battery cables, stator... not sure what else can be done? if anyone out there has more experience than i do at this or any creative idea'***** me up i'm all ears thanks.

Well a little update here. I tried everything under the sun, tested all components, and all checked out in accordance with my clymer manual. Changed batteries several times to make sure it wasn't a specific battery... I was using the smaller sized marine deep cycle batteries, like a car sized battery, not sure what the size is called, getting no more than 13vlts from the charging system on the motor, i switched to the larger style deep cycle battery, like on a camp trailer or whatnot, and it charges fine, 13-14vlts at idle, right up to 15 with rpm advance... anyone have an idea on why this may be? i realize the cranking amps and small differences in the battery but i just can't figure out what would make that big of a difference.