how to fix my speedfight 2?

I have a Peugeot Speedfight 2 2002 model which has just had a new piston and fuel tap put in by my garage, i drove to college in the morning and had trouble keeping the bike going, having to rev it alot, in the afternoon to go home the bike wouldnt start, i kept trying and got little responses such as engine starting but dieing after a few seconds, when i managed to get the revs up it would struggle to keep revving cutting revs then starting them again, there is a little electrial cable coming from the head of my fuel tap with a white connector on it which looks like it should be plugged in somewhere, any help would be gratefully appreciated cheers Jamie