Topic: 74 550K0 running really lean? [Stock airbox + MAC 4-1]

[TwoTired]

Thanks for the clarification TT.

I'll try syncing them up to the lowest vacuum carb (#4) and see how it goes.

No, sync at the lowest RPM.  And pick the cylinder with the highest vacuum (lowest pressure) to designate as master (It will have the slide that is most closed.)  Sync the others to it, even when the vac level changes on the "master" carb.  When you are done, they will all be the same.
You may need to adjust the main idle knob to keep the idle at 1000, but once you decide which is "master", leave that carb's slide adjuster alone.

[grcamna2]

   I recommend that you use a good fan blowing toward the front of the engine while you synch the carbs...for one thing, it will help blow the hot air from the front of the engine onto the carbs to help warm them up for best operation, almost as if your riding the bike w/ the wind from the ride doing the same thing.

[Dimitri13]

TT: You're right, that's what I mean; lowest pressure. So, once I set the master carb, I leave it as it is, even if it changes, and when I sync the other carbs to it, I set them at the master's original pressure, or it's current pressure?

gr: Thanks, I'll see if I can find one.

[TwoTired]

So, once I set the master carb, I leave it as it is, even if it changes, and when I sync the other carbs to it, I set them at the master's original pressure, or it's current pressure?

You don't really set the master carb, you just choose it.
The master carb pressure will change with engine rpm changes, this will occur as you adjust the other carbs.  You always adjust the others to what the master carb currently has, in the way of pressure.