hi richard,welcome to the best 126 site going!.
the ''tin rattling'' sound maybe loose bolts around the tin work......or else where,these little motors do vibrate a lot,have a good check around and nip up any bolts etc you can find,but it may be connected to your fuel question.......are you sure its not a pinking/detonating /pre ignition fault?.
the a/cooled needs leaded,or you need to add some lead additive,they are also very timing sensitive..........im sure others on here will contribute to solve your problem.........
