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Hey, moldy! Welcome to the site!

That's a grand, old bike you have there! If you'll ship it to me, I'll fix it up, give it a comprehensive test and make sure everything is in good order. You weren't planning on riding it this summer, were you?

Sorry, just kidding...

The first thing I'd check is the petcock. Sometimes the rubber diaphragm inside them cracks letting fuel bypass the carbs straight into the intake. You can test it if you can find a syringe (no needle required) or some other way of creating a vacuum. Find the vacuum tube that connects the petcock to the carb intake manifold, disconnect the manifold end and stick the syringe in the end of it, making as tight a seal as you possibly can. If you get gas in the syringe when you pull the plunger out, the diaphragm is bad. You can get a rebuild kit for it or replace the whole valve - your choice.
If this doesn't cure it, what it may need is a thorough carburetor cleaning. If you feel comfortable enough with your skills to disassemble, clean out and reassemble four carbs, then go for it. You'll need a service manual for your bike before you start, before even taking anything off. Otherwise, you better get it to a shop.

I think this is a classic case of Idle circuits gone awry ...

You have a Pilot jet, an Idle speed screw and a idle mix screw in each carb.

The Pilot jets are probably clogged (this usually happens at the fuel mix screw - the one that is supposed to be non-adjustable) The bike dies because it is not flowing enough fuel at idle. You have to open up your Idle speed screw almost all the way, which causes your low-midrange (jet needle/needle jet) to kick in, thus high idle.

You need to take the carbs apart and clen them thoroughly, especially the tiny pinholes that comprise the idle circuit. If you aren't familiar w/ carb work, I would recommend taking them to a garage to have them dipped in a chemical that will clear out your jets no muss no fuss.

If you want to do the work yourself, you will need a manual, some patience, a light touch, and you must be through. When cleaning the carbs, only do one at a time (so you don't forget where parts go), remove the whole bank of carbs (don't separate them) and use caution when cleaning. Avoid getting cleaner on rubber parts, don't use a needle or pin to try and clear the jets (you will damage them) and be gentle w/ the brass screws/mix screws etc because the strip easily.

Have fun !