Perhaps the back firing is a timing or fuel mixture issue? As rich said, it's hard to see the link between the fuel neck and the back firing but then again maybe it's because everything (bad) generally comes in three's!
I had my oil seals replaced a while ago and was surprised at how cheap and quick it was so don't fret too much about major expense. These things wear out so it's not uncommon.
At least you've got your fuel neck sorted which is a source of major ball ache if it screws up the fuel system.
Good luck
