Moped Army

So about every other time i attempt to go over a hill my moped will quit accelerating first then it just starts dropping to zero. once stopped it will resume acting normally but it is worrying me and also kind of dangerous (it happened to me on the way to work this morning on a street w/ 40 mph speed limit and a lot of angry drivers). Any ideas as to what this could be? transmission, fuel system, anything? I just got it last week and don't even know what brand it is, it has no markings anywhere but i haven't had time to take anything off of it for a close look. any suggestions will be greatly appreciated. thanks.