We flew my mates big cub yesterday. It had the re bearinged 91 in it. Problems were 1/ Spat the prop, to lean at the high end, richened up now ok, 2/ nervous driver so difficulty in getting of the ground, he got scared with the advice coming his way across the strip and goosed it now flying ok, it flies inverted no worries, and does most of the basic aerobatic card "slowly". Owner / driver now a happy chap. BTB did you know that when you fly a model inverted low to the ground and pull up elevator you end up have having an additional model space in your shed. Vale a La5 (not mine thankfully.)