Ok, I've been intermittently fighting this problem for quite a while with my 280. Occasionally the saw would just die. Restart would be hard. I could rectify it with some light L jet opening. After doing this, the saw would have a slight hesitation coming off idle, especially when fully warmed up.
Now, after I've ported the saw(it rips!!!) it is worse. I have the L jet 3 turns out and it will barely idle. Give it throttle and it dies instantly. I've tried everything I can think of. Took the carb apart and it was clean as could be, except for a very small piece of Dirko, presumably from initial assembly. Reassembled, same problem with no change.
The saw, when off idle runs perfectly. Instant throttle response everywhere except idle.