Well..... tough to trouble/shoot over the internet, but.....the fact that it runs at all, leads to the very first test......with engine stopped, does the fuel supply system hold decent pressure? ( tank pressure IS the fuel delivery process, there is NO pump).....a properly operating system will hold tank pressure for days if not weeks..... after this we can move on to fuel regulator issues (disassemble & clean) & then on to "Air/leaks" (gaskets etc.)......FWIW.....