Backfiring

Bought a bike that had been sitting for 17 years! 1984 zn1300 A2. All hoses have been replaced, got the fuel pump spinning again, rebuilt the switches, kill switch was an issue causing it not to even try and start. Now it runs and sort of idles but especially when i twist the throttle a bit it pops and backfires? Any ideas? Any help would be great!

First thing that comes to mind is a vacuum leak.  Whether carb'd or F/I , a gasket between the holders and the manifold will eliminates the vacuum leaks there. 
Sand the holder surface as shown and add the gasket (dry)
 

Scotch is on the right track. Lean fuel mixtures cause backfiring. After 27 years of sitting, gaskets and rubber components dry out and leaks can occur. Also, check the rubber flanges that hold the throttle bodies for leaks between the flange and throttle bodies. 
1.
if no leaks are found, 2 things come to mind. 
Fuel injectors have been stuck from 27 years of sitting in stale fuel and likely need cleaning. 
2. Throttle position sensor is not giving a solid signal back to the DFI Computer. It's a simple rheostat and may need a bit of contact cleaner to smarten it up. 

Thanks for the info pulled all the injectors last night to get them cleaned, but did not think about the t p s

When somebody says the engine is backfiring, to me that suggests an explosion of unburnt fuel in the exhaust system.  Is that what is happening here?

Yes I believe so as it is also throwing Flame! The exhaust does not smell rich, if anything it smells a little lean. So I thought I'd post on here get all the ideas while I've got it taken back apart try to cover them all. my first Kawasaki and I've never had one to revive that has set this long.