Well, my friend has a yz426, it used to pop last year, but just this weekend he tried to start it, and the float was stuck up so it was not getting any gas. We fixed that problem, but now when it is reved it shoots flames. My thought is that it might be lean because of the cold which would cause it to pop, but would that cause flames? My second thought is that the valves are not propperly adjusted. There could be no clearence, would that cause flames and viloent back firing? Well any input would be great. Thanks a lot.