KZ900 Idling on 3 cylinders

Mt KZ900 is only hitting on 1, 2 and 4 when idling below around 2 to 2500 rpm. I switched out the plug with #4 and no change. As I advance the throttle it hits on all 4. I just had the carbs ultrasonically cleaned but haven't discounted a plugged pilot on that cylinder. I'm off to check on that now. Can anyone think of anything else that could cause this?

Given that the plug checks out and the coil serves two cylinders the most likely culprit is a blocked or partially blocked pilot as you suggest.
Could also be an air leak on the inlet boot side or missing vac port cap which would delay that cylinder pulling fuel at low rpm's.

Thanks, I just put the carbs back on and the pilot jet is clean and clear, squirted carb cleaner through it. Will check the vac port cap.

That was it. I had been missing 2 vacuum caps when I was going through the carbs and had made a couple of them out of a 1" piece of hose blocked off with RTV and a tight fitting screw. The screw had fallen out on number 3. I'll order a set of the proper caps. It's running like a Rolex now. You guys are the best!