Unless you were to use one of the European budget airlines (i.e. Easyjet, Ryanair, etc) you will have no problem. All the major airlines seem to generally use the 50 pounds per bag X 2 bags per person rule on any flight to or from the USA and this would include the intra-European flights as long as they are ticketed on the same ticket as your flight from the USA. Be careful. If you purchase an intra-European flight on a seperate ticket that flight would be subject to the European weight restrictions which is usually 20 kilos per person (about 44 pounds) total. Also you do need to check on the carry-on specifics for each airline as that can vary (even on flights to or from the USA).