1983 kz440 won't Rev up

So I have had this bike for a few years now and think it's about time to get it running. It will start up and idle nicely. When you try to Rev it up it will spit and sputter it's way up to around 6-7000 rpm and it sounds horrible. I had the carbs off and cleaned them really meticulously. That improved it a bit but still running really rough and slow to Rev. What should I be checking? Timing? Valves? How do I tell if the timing advancer is functioning properly? Anything you guy's could tell this newbie would be much appreciated. I do all the work on my snowmobile but not very familiar with bikes. Thanks in advance for your help.
Shawn

It could be timing advancer, main or secondary jetting, or enricher circuit, or torn diaphragms on the carb slides, and probably a few other things, even fuel flow.

If it idles fine, it's probably not the valves.

If you don't have a manual, I would get one, as that will help with all of the above.

You need a timing light to verify the proper advance.

Is the stock airbox & air filter installed?

The airbox is there but there is not a filter.

Shawn420 wrote: The airbox is there but there is not a filter.

The filter is just a piece of foam.

.

I whould install the air filter. There should be a filter element case to hold the filter element & an airbox cap. Make sure the airbox cap is secured correctly. The KZ440 is known to need a properly installed stock airbox to run right.