To set the transition from idle to fullthrottle is not that hard. A great deal depends on which engine it is and the type of carb.

If it's an air-bleed type w/single needle or a 2-needle carb. The engine manual will tell you, or someone here will know. A lot of the current engines use a 2-needle set-up which are easy to work with. I have 3, MDS and 1, K&B w/2-needle carbs, and all work great when set up properly.

The second nedle is usually placed inside the throttle arm. Look for a recessed screw 'inside' the arm (it will be a slotted screw,not a phillips).

If you can, post a couple pics of the carb. It would help a lot.