I bet one problem you're having is caused by air leaking around the carb body where it slides into the engine. There is a thin O ring that's supposed to seal this but I have found that they often don't do a good job. This O ring sits at the bottom of the hole where the carb slides into and the ring sits against a thin black washer. The engine will have a hard time shutting off when you cut the throttle completely and it will cause idle and transitioning problems. There are several of us in our club who had this problem right out of the box.
First, you loosen the screw in the collar which holds the carb in the engine case. Then pull the carb out with a twisting motion. Next, coat the part of the carb which slides into the engine with an automotive sealant like Ultra Grey, Blue or Copper. Also, take out the 2 black sleeves which the carb mounting or collar screw screws into and coat them as well. Coat the screw too. Assemble everything back together and let it sit for a day. Remember you only need a light coating of sealant. you should notice a difference.

The EVO is a great engine which I think you will enjoy owning. It is well made and very reliable. I'm sure it's just a minor tuning that's needed and an air leak fix. Don't let these things turn you off from this engine. you will hear almost nothing but absolute praise for the EVO. I can't say enough about mine.