Your carbs are clogged with varnish and bad gas
The remnants of gas that has evaporated are a gummy hard varnish inside of your carburetors. You have a bit of work to do.
You need to completely disassemble the carburetors and thoroughly clean all of the nooks, crannies, jets, fuel galley's and air galley's in order to get your bike back in working order.
The entire bank of 4 carbs requires removal and cleaning. You can dunk the entire set in a 'bath' of solvent to eat away the dried up gas or 'varnish' and to soften it up. Afterword you will need to take carb cleaner and 'blow out' all of the fuel galley's. Additionally you will need to unplug your jets with a small wire and/or compressed air.
This varnish is preventing fuel from getting into your motor. You will need to clean the entire fuel system, especially the gas tank. You may have some rust in your gas tank as well. The petcock is probably clogged and may need a rebuild kit for it to replace the plastic screen. You will need to determine that upon disassembly.
Here are some similar questions and answers that may assist you in your endeavor.
Here is a carburetor removal process on a similar bike. It applies to yours.
Here is the process to clean a set of carbs with bad gas in them.
As you are troubleshooting the carbs after you clean them, you may need to identify issues to get the bike to where it is. Here is a post related to troubleshooting rich and lean conditions with your carburetor set.
After you are all done and the bike is running somewhat normal, you will need to balance your carburetors as the final step.
If you have any further questions about the issues you are experience please ask follow ups! Best of luck to you, you'll get it running again. Keep the battery on a trickle charger as you are troubleshooting so you don't take it all the way down as you are attempting to get it running.