Weaker springs did the trick! I got the Tomar Holeshot from Quarter Master directly and it came with very stiff springs (.091 ?). I probably could have specified weaker springs, but didn't know any better. I think the clone motor doesn't rev high enough to use such stiff springs. I put on a set of .065 springs and now it pulls really well. I also got a set of .075 springs, just in case, but I think these will be fine. I'm so glad to finally get this sorted out.