umm i only have to squeeze up when inverted i dont think it is a weight issue, i just put my old 140 on the scales and it was 12,1/4 pounds !! (has been repaird a lott and has a realy heavy cowl) and that stil harriers and elivators perfect and its a fair bit nose hevier than my electric one. Check the ailerons are not both drooping a bit (bit hard to see but worth checking) as it makes a big diference as does lateral ballance with the plane always falling one side and you having to pick it up will lead into wing wobble

Dave