1982 Kawasaki GPZ1100 fuel injected throttle response problems

My name is John Opp and I live in British Columbia Canada. I am a 76 year old retiree and love to work on motorcycles. Up till now, I have worked on all makes mainly from early 80's and back but recently have the privilege of trying to get my best friend's 1982 Kawasaki GPZ 1100 fuel injected bike to run properly. I was not prepared for the amount of sensors to keep this old duke running. 
   We have run fuel injection cleaner through, and I have undone the DFI connection and sprayed it with the proper cleaner. The baby starts up and runs a little rough and will take some throttle up till about 3000 rpm and then it stumbles badly, and when revved puts out black smoke. 
   Plugs are new and clean. After running they smell like gas and are a blackish color. Used my laser thermometer to check the temp of my pipes and all are pretty well the same and firing. I even used my timing light connection to check to make sure that each plug was firing properly.
   It is either too lean or too rich and i am leaning towards it being too rich because of the black smoke. Could there be some problems with the air intake or? I know there are sensors all over for balancing the mixture, so I am preparing to strip her down and use my meter on whatever I need to. 
   Any suggestions as to heading in the right direction starting from the most obvious to the culprit will be appreciated. There is only 20,000 kms on the bike and was running good last year. By the way, when I turn on the key I can hear the fuel pump loading up and click off, then she fires up. 
    It is a privilege to be able to ask these questions in a forum where probably someone has had and solved the problem. 

Hi John, have you worked through my post on your other thread and the links I included. There is a lot of information there, in the world of FI this system is actually quite basic. FI suffers from all the same things as carb motors (perished rubbers, blocked jets/injectors etc) check the basics before you go down a rabbit hole 

Sweet! And it still has the original exhausts!

check the fuel tank relief valve is not stuck/sticking it comes apart to clean, remove from tank & just push inner valve out with drill of correct size, quiet often the root cause of running rich. 

It does not hurt to clean the injectors in any case, probably has never been done.

As rangeroy mentioned those gas tank check valves can gum up, I hear some owners just took the check ball out so it can't happen. It is attached to the bottom of the gas tank to return unused fuel to the tank (return line)