1981 KZ550 D1 GPZ550 won't start

If the float valves are working correctly, they will stop the flow of fuel when the required height is reached. If the valve on the leaky carb is the problem, you will see the level go up too far, then drop when it overflows, then rise too far again.
If the leak happens when the engine is off, that means the petcock has failed, too. When there is no vacuum signal from the carb it is connected to, it is supposed to stop the flow of fuel.  Itwill need rebuilding, or replacing if the seating surface is badly pitted.
As noted, you can check all four at once, but most folks do them one at a time, adjusting as they go. The difficulty I see with trying to do them all at once, is holding all four tubes steady while you determine the level in each carb and note which ones need adjusting and by how much.

Agreed.  If I'm verifying the correct levels of all 4, I have them off the bike and on my rack fixture.  I use a rubber band around each carb to hold the tubes in position.  One at a time is easier when you'll be removing and replacing the bowl a couple times each.

Hello:The bike starts but doesn't run well. I've pulled the carbs off again and replaced the float valve needle in carb 1 with an older one that was working well. I noticed a strange difference in one of the drains/vents (can't find a diagram with the real name). One of the drains in carb 4 is either plugged solid or designed to be shallower than the other three (unlikely I assume). I thought I'd ask before drilling it. I've attached a couple of images. Has anyone else experienced this?

The clear tube method to check levels.... I remove the drain screw on the side of the floats and plug a clear tube into that, correct? Not the regular overflow drain at the bottom of the float?Thank you.Ron

Those are not the drains. The drains are in the bottom of each float bowl. The bottom of the carbs that have been removed in the pictures.

www.kzrider.com/filebase-alias?task=down...&id=579&catid=26&m=0

Hello TexasKZ:

Yes, you are right, its not the drains shown in the images. I think the vent or whatever I should call it is just blocked.

Ron 

Hello:

I still have a leaky left (#1) carburetor, which nothing I've done will stop. I guess I'll need to start over again this time with a full set of OEM kits, can anyone recommend what is a good kit OEM maker? HowardB suggested #97 jets with the clip in the third groove and go back to the standard airbox, I'll try that but it's such a bitch to get the carbs squashed in between the airbox and the cylinders.

Ron