1978 Mercury Cougar XR7 review from North America

This car was given to me by my grandfather when he passed away. Now I am 17 and I drive it almost every day. We had the engine rebuilt at 100,000 miles.

My dad just recently put a new carburetor in it, about 2 years ago, and whenever I first start my car, whether it is summer or winter, when I hit the gas down to the floor quickly it goes high then goes low like it will stall, but comes back up again. After warming the car up for about 10 minutes, I go to drive it. When I floor it while it's standing still in Drive and hold the accelerator down all the way, it stalls out completely. When I do the same thing, but let go it comes back up to a normal idle. This does not happen if I let it warm up for at least 15-20 minutes. My dad told me they call this a "cold spot". Can you tell me how or why this is happening and how to fix it please?