Piaggio NRG MC3 Problems, Help would be apprieciated. Cheers

Hey i just bought a Piaggio NRG a couple of days ago. As far as i knew it was running fine when i bought it... been riding it for a couple of days and seemed fine except would take quite abit of throttle to go but then would just shoot off and sometimes cut out when running idle but i thought that was just the revs set to low or something and would be ok when warmed up. Today it started losing revs and power when i was riding. i let off the throttle and pull back and it would go again. i got it home and when i tried starting it up again it wouldnt. i got it started once and it wouldnt go anywhere, i had the throttle pulled right back but it only just kept the engine running. now wont start up at all. i dont know much about bikes but i had a look anyway and i at first thought it might be the throttle cable but i had a look and seemed fine. i went to look at the sparkplug and what it goes into (dont know the name? lol) there was this gum stuff at the bottom which i thought was odd, it was hanging off slightly already so i pulled it off to see what it was hiding, there was a crack that has been welded. i thought this may be the problem like the engine losing compression or something? if not anyone got any ideas? this is the first ped ive bought and i think ive been had! seems like a quick bodge to me? any ideas? cheers, Kaz