Built a mb W/ my 14 y.o. son as his Christmas present. Have logged quite few hours in the garage fine tuning & tweeking the setup on his beach cruiser. We are having trouble keeping it running, a carby issue. The carb is flooding and fuel backing out thru the air filter. have dis & re assembled the carb. Tickler is NOT stuck (we don't use); float is free; air/fuel mix screew has been seated & backed out 3.5 turns; carb is nearly perfect level to ground. OF NOTE: fuel floods thru that air filter even when not running until shutoff valve turned. Need to gets the machine to go & keep it going for my young man. Any suggestions???