Yup, if pinching it causes it to accelerate like it should, then the low end is too rich.

Someone may have adjusted the low end idle too far in an attempt to cure transition problems.

The SuperTigres are notorious for mid range problems, that often can be fixed by adjusting the mid range...

( Yes you CAN adjust the mid range on most SuperTigre engines seperately. )

Check the SuperTigre faq pages for infor on this.