these type of fires are prone to sooting up because the manufacturers deiberately restrict the supply of air to the burner to give the realistic coal effect flame, this means that even a small amount of further restriction to the air supply can lead to sooting. it is for this reason that this type of fire should be serviced at least once a year.
it is very important that if you ever take the coals off to clean them that they are put back in the correct positions as shown in the fires instruction book. you must never add extra coals, never swop them for pebbles, and if you replace them you must buy the coals for that particular fire.
as for the burning around what is the primary air port, its difficult to say without examining the fire but the burner could be blocked, it could be cracked or it could be suffering from flame reversal, of there could be small gs leak on the fire.
you really need to call out a gas engineer as soon as possible. to give you an idea we charge �40 for a basic service on an inset fire but the going price seems to be around �50 to �70, i believe british gas charge around �79.
if your in the birmingham area then give me a shout.