why does it seem slugglish and why dont the indercaters work?

i would like to know why my moped seems sluggish, it starts off fine then slows down then speeds up and repeats the cycle, also my indercaters dont seem to work when the bike is running fully but seem work when they wont to we i am staying mobile, please someone answer my question as it is driving me mad. the bike is a Gilera Runner 49cc.