I would say you are getting vapor lock. The fuel line under your vehicle near the exhaust is getting hot enough that the fuel vaporizes in it and can't be pumped. This causes your carb fuel levels to drop radically which then causes large changes in your fuel delivery to the engine. If you were in motion the air passing under the vehicle would be enough to prevent this normally. Then as you actually accelerate these areas of vapor show up at the carb spurt, bubble, spurt, bubble, spurt, causing exactly the symptoms you are reporting. Soon the air cools the line back down and away you go.

To fix this you can:

1) Try putting an electric fuel pump in/near your tank. This helps but not always.

2) Put heat shields on your exhaust pipe ala like what's on motorcycles to prevent leg burning.

3) Put a heat shield, sheetmetal, next to the to fuel line.

4) Re-route the fuel line.

Good luck.