1998 Honda Accord engine losses power when its warmed up

1998 Honda Accord mileage: 87,000. My car starts off well when it is cold but the moment it warms up the engine loses power. When I warm it up in the morning for more than two minutes, the engine does not respond when I step on the accelerator pedal. I have to keep pumping it for the car to move. When I drive off and start reach about 70 mph, it begins to hesitate and the engine stops responding to the accelerator pedal. After slowing down to about 45 mph, it begins to respond again. Holding the accelerator pedal to the floor sometimes yields a positive result. It has a carburetor and I have been told four times that it is not a carburetor problem by my mechanic who also gave the car a complete tune-up. Now he is telling me it is the distributor. However, this car has traveled to NYC from NH two times. Please help.