What is causing "Bessie" to hesitate upon acceleration.

What is your question?

When i start to accelerate at a stop sign/light, "Bessie" sometimes just hesitates and I'm sitting there trying to get moving. People behind me Beep their horn or yell. After a few pumps of my foot, "Bessie", will eventually get going. Then, during acceleration, she has trouble getting going. hesitation again. Whats the problem?