If it's shortly after start then you need to adjust Uaccel1 upwards. If it's more like half way thru the start then you need to adjust Uaccel2 upwards.

Hold down Limits and press the right arrow (+) to get to the pump menu. Use the right and left arrow buttons to move thru the menu. Hold the change button and use the right arrow to bump up the appropriate setting 1 or 2 steps. More if necessary, but it will start showing a little flame out the back if you go to far.