3W engines in and of themselves are not "finicky". If you're having a problem with a finicky 3W, look to the carb. Tuning a Tillotson takes time and a lot of patience. They also don't like to maintain a set position for some reason. Many have found that changing the carb to a Walbro has brought modeling nirvana to the nose of their planes.

In tuning carbs, wait until the engine warms up a bit before turning the needles. The larger 3W's don't warm up especially fast, so working the needles too early provides a false setting.