Dazxs250

hi guys. im a noobie here so dont know if this is the right place to post my xs250 1981 wont start just backfires now and then, just replaced the points and right side coil, all wires been cheaked new plugs and leads and had a mobile mechanic here this morning he set the points and timed it but nothing happens. plugs spark ok and points spark a tad weak any help would be great. thanks Daz.