[zac]

Could be the power piston stuck in the up or rich position. Sometimes varnish forms in the piston bore and it sticks so that it can no longer respond to vacuum changes, so the primary metering rods can no longer do their job. You can see the top of the metering rod hangar if you look down the vent (that tube on top of the carb). You can put a very small screwdriver down there and push the piston down if it is stuck up. I