When i take off it drives really well but soon after about a 2 mins or so it starts losing acceration, like it dont want to go but it picks back up again . I have just installed brand new Carb what do you think might be causing this

 

have you checked the etc?..mine was having issues of bogging and stalling after running my 300 hard...rebulit carb and same thing...the i had a bit of play in my throttle cable and it was messing with the etc switch