^^ 2nd This.When you rebuilt carbs, did you remove all orifices and clean passages/right size orifices in right holes/remove welch plugs for idle transition circuit and clean and install new welch plugs? Verify proper orifices? idle-34/mids-34/mains-58.5....early first year XP/GT 150's had a 1 3/8 carb. Check and see if they havent been swapped out. 1 3/8 stamped on the front lower right of the front of carb. Once we verify the fuel system, we can move on to other fun and exciting things,,,