More stuff comes in through your tank vent than you might realize. Use the walbro filter, do not use an automotive filter with premix. A small air bubble in the filter is not a problem. You can orient the filter vertical to remove the air if you want.
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience