What 2 into 1 intake are you picking up?
The jetting should be pretty close if it comes with the intake, no?
Once you get it, pull it apart, find out what needle, needle clip position, pilot jet and main jets it has in it.
I lik to replace the phillips screws with sst socket head cap screws, ie., allen head screws.
Buy a large can of Carb Clean and clean out the carb completely.
I like to verify that fuel does not overflow out of the bowl.
This would indicate a faulty needle and seat valve in the fuel inlet.
Trinity sells 2 into 1 intakes that run the 33mm PWK Keihin.
Call them and ask for Joe. http://www.trinityracing.com/yamaha-banshee.html#intakes
He's cool, he rides and knows Banshees.
He'll get your tune very close over the phone.
The more info you give Joe about your setup, ie., elevation, type of riding, average temp, mods, etc, the more he can help you.
If they ask, just tell them its their product that you're bought used online, Joe should help you out.