My friend is in spain now, his tt600r is not running well. Starts Ok, runs and revs ok but is backfiring. After riding at speed it starts to die, eventually stops. But it will fire up ok and run straight away. What could this be? All electrics seem ok. I am thinking maybe a fuel blockage of some sort?

Any advice would be appreciated.

There are a few things to check.
1. Check that gas cap is venting properly.
2. Check screen on fuel valve inside tank.
3. If it has an in-line filter, check.
4. open carb, check float and float valve.

That's the easy stuff to check first.

If it's got two carbs like TT600re check rubber diaphram has not split.