No doubt a better engijne will give improved performance - I normally use either OS 46FX or ST51 on mine - but a 40LA will get it up and flying if it's built correctly. My most recent one came in at 6# 9.6 oz., so if his is close to the 8# mentioned he may well need a different engine. I'd also be concerned about the CG - there may be too much nose weight keeping it from rotating. Also, some folks smooth out (round off) the step, when it needs to be a sharp edge. A rounded step causes significantly higher drag.