I never got around to clipping springs when I ran a BST40. I did like the idea someone mentioned of using dental floss to temporarily tie a couple of coils together.
One thing which worked out well for me was to use an intake divider on the BST40. It made it quite a bit more responsive off-idle. I liked it a lot, but my install was careless and it ate itself. Hated the carb without it, so instead of building the divider again I started trying different carbs; HSR42, TM40 etc. To be honest, after all this time and effort, I kinda liked my modded BST40 the best.