The main concern with the design of SuperTigre engines was good top-end, good idle, and a transition and midrange that works. It is very, very difficult to make a model carburetor act in a linear manner. To do so, usually costs more money. Also, it may help to get better fuel pressure. Higher pressure means you can lean the low-end needle more, and this helps. The 'Tigre engines really weren't designed with 3-D needs in mind.

Also, please be aware that your engine's performance will only improve as it's run. It usually takes 2-3 gallons' worth of running to get them to really come in.