They work by sqirting gas (I'm assuming that you are not talking about gasoline, but propane or equivalent) through a tiny hole called a jet, and mixing it with air in a tube which goes to the burner.

Dirt/spiderwebs, etc, can be introduced when the hose from the tank is disconnected, and partially block the jet from the inside.

Solution: Take the barbie to where compressed air is available, dismantle it, (many come apart without tools) unscrew and remove the jets (They look like tiny brass bolts with almost invisible holes, usually) with a spanner/wrench, and blow the jets out backwards, and blow everything else out just on principle.
Do not enlarge the jet holes, they are critically important. Wear glasses when using compressed air. Turn on the gas tank knob VERY briefly to evict any residents in the hose. Do this out-of-doors, and don't be near naked flame when you do it, because gas will hang about near the ground.

This is a fix for the generic barbie.
If there are any holes rusted in the tubes, or burners, or cracks in the hoses, as Liz says, in yours, it could be very dangerous, because the gas hangs about near the ground, being heavier than air, so the first thing you know, you are PART of the barbeque.


I've just re-read this, and it is quite frightening to the uninitiated. This was not my intention, but caution is advisable. Propane is remarkably dangerous, so don't take ANY cances with possible leaks.