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I didn't ride her for over a year and when I finally did try it would barely crank. All the internet wisdom said old gas had gummed up the carbs, so I first tried a pretty superficial cleaning. It did run a bit better, but slowly degraded to its former self. Try #2 involved a full jet kit. It ran better than new, but also lasted about a week. Try #3 involved rebuild kits and the service manual. I removed everything that was removable, replace all o-rings and the other stuff that came in the kit to no avail. Didn't start out running as well as #2, but didn't last either.

I've drained/replaced the gas. Fuel pump seems to work well.

I'm pretty sure the air box is seated properly. That is mentioned in the manual as a probable cause. That's a b1tch for me to do and see if it's right. I've noticed that by running it with the tank up, I can cover just the right amount of the top air box opening with my hand it runs much better, so I still wonder if it's air flow related. I'm no mechanic, so any help is appreciated.

Sometimes that protein sludge stuff from ethanol can be problematic. But check your tank for rust and/or a plugged vent first.

Also make sure to replace your filter... Sometimes an old filter can be more restrictive than it looks to be thanks to oil and fuel residue gumming it up. Then check your fuel hoses for any signs of degradation. If they start degrading thanks to the ethanol in fuel, it can gum up your carbs really quickly.

The inside of the carbs look clean enough to eat off of. They have new jets, gas and o-rings.
Can't see any rust in the tank.
The tubing looks ok from the outside and seems very pliant. The bike is always kept inside.
If the air filter was clogged, I can't see it working on the first day 3 times.

Forgot to specify: It will idle, but dies/backfires when I try to give it any gas or take the choke off.

fuel has to be

It's not the gas, fuel screen, petcock, pump, tank rust or tubing. Any other air related ideas?