I have a few on these and they don't really break-in until upwards of 2 gallons then they really come to life and you don't have to fuss with the needles. Until then you need to make very small adjustment to both the low and high needles. Sounds like the low side is a bit lean. Try opening it a little and then readjust the high needle.
If using the factory blue filter, make sure it is not leaking as I had one that did .
Take the factory muffler apart and reassemble using red high temp sealant on all of the surfaces, retainer bolt, and header/bolts.
Make sure the tank height is correct.
Make sure the plug cap is locked on with a slight twist.
If it doesn't improve start from the beginning and reset the carb barrel and the low/high needles to factory specs and re-tune.