Welcome to the site !!
The first thing I would check is the Coil Wires ( 2 of them) , the 1 that goes to the plug itself and the power wire at the coil itself , usually when removing/installing the gas tank , the fuel valve gets hung up on the power wire when pulling it thru when removing/installing the tank , it then either makes no contact (wont start at all) or its just on it but loosely and getting intermittent contact , especially when the bike is revved ................... So basically , you need to either look under there from the ignition side of the engine and look up under the tank at the front of the frame where the coil sits and see if the coil power wire looks like its not on all the way or crooked , or better yet gently pull on it and see if it falls off ...... You may have to remove the tank again to correct the connection , and that would be a good time to look at the plug wire and make sure it is on all the way ........ Those would be my first guesses as to why its doing what it is doing , if you adjusted or changed nothing else .........
When reinstalling the tank , use your hand to guide the fuel valve down to the corner where it comes out , this way you avoid getting caught on the wire and pulling it off ....