No effect when you goose the gas? Dirty (clogged) gas filter, clogged brass filter sock in the bottom of the tank, carb floats/needle valve stuck? Sounds like a fuel issue to me.
Do you have an electric fuel pump? If so do you hear it run at startup and then occasionally?
Do you have a vent to fuel tank? Either a vented cap or a small hose off filler tube. Try running it with the fuel cap removed. Could be vent is blocked.