My mower has a briggs and stratton 158cc, 550 series engine. The atomatic accelerator has quit working?

The mower is 1.5 yrs old and has mowed the yard about 12 times. I can start the mower, but to keep it running, I have to manually accelerate it. When I let it go, the engine idles down and then dies. The old ones used to have springs attached to the accelerator, but on this one, the linkage goes to a cam which sets on top of the engine. Do you know what causes this? Thanks