Several years back,I had a Hellcat and I used a G-62 in it and had the same problems as you are having..I switched to a Sachs 3.7 and that made all the differnce in the world...I would highly recommed a 3.7,but if I were to build another one,I would install a 4.2..can't go wrong on that combo........also was using a Zinger 22-8/14 prop on the 3.7.....good luck