1980 Kz250 won't rev over 4000 rpm

1980 KZ 250 with a Keihin CV32 carb. Bike won´t rev past 4000 rpm. It gets there and just dies. I have cleaned the carb, adjusted the timing and valves. Everything is clean. The bike idles great but when I throttle it up to 4000 rpm it just dies. The main jet is clean and the bike used to run great. I let it sit for two years, but have since cleaned everything. Is there some passage in the carb I am missing when I cleaned it?

I just did a test on the carb by putting a vacuum to the engine side and opened the butterfly valve. The piston behaved as expected, it was raising and lowering as I opened and closed the butterfly, and gas was shooting out of the main jet in a fine mist. I am stumped? Any help is appreciated

Not only is there a big main jet for fuel in your carbs, but there is an "airjet" that is connected to the main jet passage. Its usually found in the back of the carb bell(where air filter bolts on)
You should see 2 small brass holes . The bigger hole is for pilot air(lowspeed) and smaller hole is for mainjet airjet. Make sure they are open and not clogged.

Also check your float level in the carb and make sure you dont have fouled spark plugs.
Some CV carbs (vaccuum operated slides) have the air jets under the rubber slide diaphram if you dont see them in the rear of the carb bell.

They are in the rear of the carb bell. There are three. When I spray carb cleaner in one it comes out of the main jet, another feeds the pilot jet and the third one feeds the secondary jet. They are all clean and the cleaner flows out of each appropriate jet with a healthy spray.

Oh, and the float level is what it should be, approximately 3mm below the bowl seal and the plug is brand new.

If you have points, maybe look at your points and timng as well....plugs look good? Have you checked fuel flow coming from petcock? Do you have clean fuel filter. It sounds like a no fuel situation as well.