Sounds like a stuck float valve. Did you replace the fuel filter? Take a look inside the tank and see if you see a shiny bottom of the gas tank interior. If not, and it has
not been coated with an aftermarket tank liner product, you are supposed to have a shiny-metal interior. If it's rusty or gummy, you will continue to have carburetor problems.
You can use a long socket extension a 3/8" or 1/2" and give the float bowl/carb body a few
thwacks to try and dislodge the debris that is stuck between the float seat and the needle valve which controls the flow of gas into the carb.
There are plenty of threads on here about cleaning a gas tank. My advice: read the threads about it, and decide which one is the one you would have the best success doing.
My advice is to remove the gas tank (use the search function, upper-right) and to do a 'cleaning vinegar' cleansing of the fuel tank. If you do that,
do not leave the gas level sender in the gas tank! Remove it and install a blank-off plate, which is easy to fabricate. Home Depot sells 30% cleaning vinegar, 1 gallon container, but you can use a 6% solution, and have good results in a couple of days. Much cheaper than Evaporust! Much less dangerous than electrolysis-I would never leave an electrolytic cleansing unsupervised! And the vinegar is less caustic than any type of acid, and easier to dispose of, safely. Read the threads.
Whatever you do to clean the tank interior, you have to
immediately rinse it thoroughly, and dry it, as it will start to flash-rust in < a half-hour! If you aren't going to be immediately re-installing the tank and trying to get the engine running, you can even use used engine oil to coat the insides until you are ready to work on it again. The tank has a drain, but it's hard to locate on the bike as the OEM exhaust resonator is directly-below it.
Let's say you cleaned the tank, but were going to install it another day. You put some oil into it, and turn the gas tank all-around to thoroughly-coat the insides. In a couple of days, you return to drain the gas tank, and install it. Drain as-much engine oil out the drain plug as you can, turning the gas tank every which-way to drain as-much oil as possible. Re-install the drain plug and the fuel level sender, and then the gas tank. The small amount of oil on the tank sides/bottom isn't going to cause you any issues, just throw in a gallon of gas.
Don't connect the fuel pump to the carburetor. Pump out some of the gas from the gas tank into a clear container, to see what gets flushed-out, and do this with a brand-new fuel filter. After you're sure the fuel is clean coming-out of the fuel pump, then hook it up to the carb gas line in, and see how it fires-up.
If it was my bike, I'd probably have also pulled the carburetors, removed the float bowls and the jet blocks, after breaking the carburetors into two pairs of two carbs each (L & R), and have removed the jet blocks to clean the two brass jets in the jet block (for each carburetor). The pilot jet is a tiny orifice, and all it takes is some granular sediment to plug it solid. That causes problems in starting and idle/off-idle operation, and throttle response. You can try the 'peashooter' and the 'shotgun' methods all you want, (more topics to search-for) but jet block removal, and cleaning of the pilot jets and the main bleed pipes, and carb passages is how to do it properly.
