1- pull the plugs
2- look at the plugs
3- one or more will be black
4- replace the plugs
5- ONLY AFTER you replace the Injectors
With as much carbon and soot you are showing, it looks like your injectors are dumping fuel. Likely failed due to alcohol as they are pre 93.
Your ZR-1 requires basic maintenance including plugs and injectors. It is 28 years old.
I would also agree with an earlier poster that you also likely have leaks at the injector housings, but start with the simple stuff, if injector replacement resolves the issue, stop there. If not; then have a round two.
Marty