I just bought a NEW Coolster 3125XR-8, when my son tries to bury the throttle boggs down and stalls. We've tried to slowly work the throttle to maximum and still no luck. Everytime we bury the throttle it stalls. There isn't any carb adjustment so does anyone have any idea what to do?

 

Do you know if this is a carb with an accelerator pump, or is it a CV type carb? If a CV carb, the slide is raised by vacuum on a diaphram on the top of the carb, a hole in this will prevent the slide from raising, bogging it out. If it has an acellerator pump, it could be stuck down, so no extra fuel is getting to the carb for acceleration, this will cause a bog on take off, but if you are sitting in neutral and slowly revving it, it should still rev out with no load on motor.
One other thing to check is to see if the choke is stuck closed, this will make it very hard to rev up as well.
Give those a look and let us know what you find.