the rear brake on my mates sy250 2002 has no power i have put a new slave cylinder piston in it and bled all the air out but it will not apply the brake the pistons move a little but not enough to bite any ideas

The master cyl must build adaequate pressure. You never said wether or not the pedal is firm. I went round and 'round with a little 200 Gasser once which had a cracked rear brake caliper housing. It had weak braking and seemed to leak a little only on occasion but never had a decent pedal either. (mushy) Also make sure the caliper is aligned with the disc. Pads and caliper housing must run paralel to the disc. You may need to put a rebuild kit in the master cyl,. Be sure to have a small amount of pedal free play before attempting to bleed it with a syringe , pushing fluid back through system from the bleeder screw seems to be the best way, or with vacum pump. Once system is bled properly and has good firm pedal it is time to wet her down with the hose, drag rear brake 'til hot and repeat as many times as needed to get a nice bite from the pads. Let us know how it goes, JL

hi thanks for the suggestions sorry i took so long to reply computer broke going to try some brake pads as his are quite worn