I'm new at this and have no idea where the settings are but try this,give the engine full throttle and let it run for 30 seconds for warm-up,then adjust the high until it bogs down then back a quarter turn,let it idle then go to full throttle,if the engine hesitates turn the low end screw out 1/16 of a turn at a time until it doesn't bog down,if it's cold it will probably bog down tho.Then back to full throttle and adjust the high again,let it idle and if it hesitates going to full throttle,then richen low 1/16 turn until it revvs up smooth.The air bubble has something to do with the pickup line in the tank,one thing you might try is going to a smaller id line from tank to needle .Just a thought but others will have inputs as well.