It seems like the anemic front brake on the 250 is a constant topic around here. The brake on my bike was no exception. It barely contributed to braking and the action at the lever felt dead. After extensive eBaying I finally had all my parts in one place today so I tore into the system.
I removed the master cylinder from the bars, pulled the brake line, and the front brake caliper. I repeatedly flushed the MC with fresh DOT 4 using a syringe and clean rags. I completely disassembled the caliper and after flushing it installed two new seals for the piston and lightly honed the piston. I bolted up a Spiegler steel braided line using new banjo bolts with speed bleeders. After reassembling the caliper I installed SBS brake pads. Before reinstalling the caliper I gave the rotor a thorough cleaning using acetone and steel wool.
I used a cheap one man brake bleeding tool and the system bleed up easily.
The end result is remarkable. The front brake will lock up now and provides the majority of braking action, as it should. More fooling around using different parts may provide some improvement but my experience is that before heading in that direction it might be best to get the existing brake working as it was designed to work. The money I spent on the banjo bolts with speed bleeders IMHO, is money I would have been better off spending on something else.
Hope this helps.