Sounds like the choke plate isn't getting to the full-open position on time. I would say that within no more than 5 minutes, the choke plate should be full open if it is an automatic choke.

It may use a bi-metal spring to operate and it should be adjustable....observe the operation of the plate during warmup.
Don't burn your whiskers off

If it turns out to be a choke problem and the automatic function can't be made reliable, you can install a universal, manual choke control.