Speedfight Problems?

I am having problems with my peugeot speedfight, the main problem seems to be it is not gettin enough power through the bike, it will accellerate and then loose power at the top end, it will stick at thirty and if it goes any higher it start to judder, the only way i can describe it is that its kind of bunny hopping, im really confused, also there is oil and fuel leakage from somewhere on the bike and its going onto my tires and exhaust i have no clue where it may be coming from please can you help me out asap, i have just put in a new drive belt, i was hoping that would help, oh yes and also it is backfiring and also the electric start will not work, i put it down to the cold weather with the battery but its all becoming quite a big problem, write back please with your sujjestions thanks very much :)