I have the same problem. well, similar.

B280, starts right up when cold. The past 2 times
I've taken it out, it runs horrible, blue smoke, rough
idle like it's running on oil instead of fuel, trying
to shake off the motor mounts. I let it run that way
for awhile and tried to discern any obvious problems
and finally gave up and restarted it, and low and behold
it runs fine.

So seamingly the 'choke' is stuck or perhaps the knock
sensor is hosed. who knows.

Ahhha, Thanksgiving here in usa, and i went to friends
for turkey and fixings, on way home it did it again,
upon investigation, I found a damn vacuum hose loose
from a T at the base of the drivers side (left hand
side drive, ya aussie) strut tower. Plugged that stiff
fucker in and shes runnin like a dream.

good luck