Can we assume the old carburetor didn't do the same thing? Worn out or something? Why did you replace the original carburetor?
Where did you get the new one? If it has some sort of warranty, take it back and excersise that warranty. You paid for it.
If no warranty, have you gone through it to make sure everything is set right? Do you still have your old carburetor so you can compare parts like the jet and so forth?
Did you check the float level? make sure it isn't stuck?
Buy a quality rebuild kit, take it apart, rebuild it, and make sure everything is set up precisely as the Engine FAQ rebuild and adjustment procedures outline.
CJ