stops at 4K RPMs

Thanks to the guys who helped get my carb problems sorted out!
Got the bike running and no more gas leaking...but it wont rev over 4K RPMs?? Accelration is fine, idle is fine, but I just cant get the engine over 4K RPM's?
Its a KZ750N.

I feel like I've seen this kind of thing before in other threads. The advancer not working right can cause top end power loss, but I wouldn't think it'd be that severe. Try running with the gas cap open, sometimes they don't vent right, and it starves fuel. Is it like a sudden drop in power, or is it just tapering off to where you can't go any furhter? Same in every gear?

Just tapers off, wont rev over 4K, no matter what gear I'm in. I'll try the gas cap trick.