Wont start peugeot 206 1.1 zest 2005?

Good spark new plugs, wet plugs, cam turning, battery fully charge. Just backfires in air cleaner now and then?
And now refuses to start was running fine. It was then left to freeze up and now it wont start! No leaks on the cooling system and seems sound. Electronics? It just as though the igntion or valve timing is a mile out !