I'm not sure what you mean by an adjustment of the gas, the flame profile when the oven is lit and when the door is oven is perfect.
The burner appears to run out of air or the waste gases are not being evacuated.
The input gas pressure is 20mb what other adjustments are there. This a BRAND NEW APPLIANCE my customer wants to use it. She doesn't want to wait weeks if this is something simple.
Is it possible that a flue or something like that is blocked.
Best Regards PAUL GREENE