Running rough/dropping cylinder

Hey everyone! Had an issue with my 1981 kz650 car running rough and dropping cylinders. Tested everything electrical and all spark is strong. Cleaned the carbs only switched which cylinder was dropping (jets were pretty fouled up after cleaning recently). Had a spare engine that runs well and we even switched it and still same issue. It seems like it has to be the carbs but everything looks good after a cleaning. The choke used to have a lot of tension in it and now there is almost none, could a broken choke adjustment cause this? 

The plugs will tell you if it’s a fuel problem. 


EDIT: Actually all you proved it not the engine. Still is some other system on the bike. Electrical, spark, fuel.