Something don't seem right...my new AP Wasp .061, still tight, pulls a 200 sq. in. combat wing on 48' lines plenty fast. It isn't the equal of my Norvels (not yet), but a strong engine.
I can't imagine an .061 not pulling the White Lightning easily, even on longer lines. Perhaps your prop choice is hindering it? I use 6x2, 5.5x2.5, 5x3, 5x4, 3-blade 5x3, depending on the speed I want. These engines like to rev, don't lug it down with too large a prop. Just a thought.