A double pumper carburetor is two carburetors in one. It has two separate pumps, one for each cylinder. The advantage of this design is that it can deliver fuel at a higher pressure than a single pumper carburetor. This means that the engine can get more power from the same amount of fuel.
However, there are some disadvantages to using a double pumper carburetor. One is that it is more expensive than a single pumper carburetor. Another disadvantage is that it is more difficult to tune and maintain than a single pumper carburetor.