Thanks for the review Fish...
I had considered doing some mods to increase the torque on my son's XR-70, but he's 9 and I think that he will have outgrown it by next season. The cockpit area is getting really tight for his frame, especially for standing up during woods riding. I have considered getting taller handlebars, but have resigned to the fact that a larger bike is in order.
The next bike will probably be an XR-80, which I hope will last for a few years. Wonder why you didn't go with an XR-80 yourself? Manual clutch? And I wonder how the power of an XR-80 compares to your punched-out XR70?