My motorized mountain bike idles VERY high like its going to blow up when I idle. It seems to do it mainly if I give it give it a little gas when idling. I tried replacing the carb with a "rebuilt" spare, replaced the fuel cable with a brand new one, and took off the twisty throttle and put a squeeze handle on instead. It still idles high as ****. The carb is on all the way and tight, haven't really checked for tiny cracks in the motor for an air leak, but I scanned it for big cracks and nothing showing. I even tweaked with the air/fuel knob, choke, and all that and nothing is working. I hope it's not a cracked motor.