I had this same problem before, what i noticed was that after about 20 pulls i still didn't get any fuel into the fuel line. I had to resort to dripping fuel directly into the carb.
The engine would start and then die soon after.
Turned out the high speed needle was closed in too much i had to open it in increments of 1/8 turns until i had it about 3/4 turn open. Try this giving the pull start
a pull after every 1/8 turn opening, eventually the fuel came up quite easily!!