The simplest fix is to install a .46LA and save the .40LA for another smaller plane down the road. The .46LA is built on the same crankcase as the .40LA so it will bolt right in and, yes it is much more powerfull. It weighs about the same (.1 oz lighter) so C/G won't change but you should check it anyway. Your observation of an "under powered" problum is valid when flying this aircraft/engine combo off grass that in any longer then a putting green! The other suggested engines will also fix the power problum but may not be as direct a bolt in replacement as the .46LA will be. Changing props or wheels still using the .40LA won't fix it, "been there done that !"