If the flame is (almost) all blue and a good shape, and isn't leaving carbon on the load, it's probably OK. (But should always have a CO detector. Cheap insurance.)
If it's leaving any carbon (black sooty stuff on your pot), that's a clear sign of incomplete combustion. The goal is to get all carbon to CO2. If O2 isn't getting in, you can be left with CO and carbon deposits (and other stuff).
Reasons vary. Damaged/rusty nozzles, improper gas pressure, blocked burner (i.e. pot too close to burner) are common reasons. Enclosed appliances also need proper draft, meaning the flue needs to be the right height/shape/size and need enough makeup air.
If it's leaving any carbon (black sooty stuff on your pot), that's a clear sign of incomplete combustion. The goal is to get all carbon to CO2. If O2 isn't getting in, you can be left with CO and carbon deposits (and other stuff).
Reasons vary. Damaged/rusty nozzles, improper gas pressure, blocked burner (i.e. pot too close to burner) are common reasons. Enclosed appliances also need proper draft, meaning the flue needs to be the right height/shape/size and need enough makeup air.
