Check the filter on the fuel on/off switch under the fuel tank. This bit me. It can be removed without removing the tank - two bolts.
Fuel problems can be deceiving as the sediment bowl will appear to be full, yet the carb is getting no fuel to provide to the engine.
Also, the sputtering on mine was fixed with carb adjustments. The manual says the initial setting is 1 1/4 turns (high speed adjustment screw), but mine ended up about 2 1/4 turns to correct the problem. Idle must be re-adjusted after the high speed is set.
Hope this helps,