1. When you say run it for 5 mins, do you mean until its hot?
2. And when its hot, does it run normally, or misfire? if it misfires, maybe a cracked dizzy and is only affected under heat
3. When you go to start it again after 5 mins, is the fuel pump priming or not? could be an accumulator fault
4. Is the starter actually turning but its not firing, or is it not even turning over?