I have an 1981 motobecane romp usually rides just fine. Recently, right after I start it up and start pedaling off there is a strange, continous clicking noise that doesn't stop then it stalls, sort of. I found that the chain had been dry and had fallen off so I greased it up and put it back on. Now after I start going the bike does the same stalling thing, slowing down. I started taking the thing apart but I'm not sure what I'm looking for-I'm not sure what it could be. I'm very, very new at all this so please be patient with me and spare some knowledge....?