CV40 or CV44 needles will not work in the CVK carbs, totally different, however the CV40 springs are a good upgrade, allow the slide to rise faster, if you change springs you have to drill the vacuum ports also. The springs are softer, less tension, therefore will allow slide to rise quicker, but must enlarge vacuum port to make it work right. CVKs are vacuum assist slides, CVs are not same, although similar in design. The CVKs are simply a "whimpy" carb, not very responsive like the CVs.(Accel Pumps).
