I'm not familiar with the 350, but I have a 200 and an Omni 3000 both of which are bottom feeders.
Check and make sure you have a good flow of air. Hold it close to your hand or the surface of some water and just blow air through it and make sure the airflow is smooth and even. If you have good airflow then it has to be something in the paint path.
There is a vent hole in the cap of the bottle. Make sure that hole isn't covered by the inner seal of the cap or plugged with paint. Also make sure the siphon tube that goes down into the bottle is clean and free of clogs.
If that doesn't help, disassemble the paint tip and soak all of the metallic parts in laquer thinner overnight. I can't tell from the picture whether all of the parts of the paint tip are metallic or not, and I'm not certain whether the seals are solvent proof on that model (I'm about 99% sure that they are, but not 100% sure).