Husquvarna 266xp won't run once warmed up?

My Husquvarna 266xp starts fine cold. I've optimized carb. settings for my elevation. Spark arrestor has been removed from muffler. New air filter, plug, and fuel filter. Problem is, once saw is well warmed (5-10) full-on sawing the saw sputters as I beging to throttle up, and takes about 20 secs. to hit full throttle. Fine then if I keep it at full throttle, but if I let it idle, it either dies, or takes another 20 secs. to get to full throttle again. Help!