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It could be an 1981 KZ650-F2 engine. The engine covers are those used on the 1981/82 models and it has no kickstarter. The 1981 KZ650-H1, 1982 KZ650-H2, and 1983 KZ650-F3 would look the same as the KZ650-F2. Prior to 1981 the KZ650 had a kickstarter, and in 1983 the engine covers changed so they didn't have "Kawasaki" cast into them.

Regarding the carbs - according to the parts diagrams and other references the CV carbs came on the 1982 KZ650-F3 and 1982 KZ650-H2, but the 1981 KZ650-F2 and 1981 KZ650-H1 had VM24 Mikuni carbs. So either someone switched carbs or the engine is from a 1982 model.
Ed

The carburetors are probably form a 750-4 --- maybe from a 750E. ???
For comparison search eebbaayy for 1981 KZ750 carbs (or 80 or 82).
The 82-83 650s came w Mikuni BS32s.

Here's a site w a manual --- the carburetor info may be helpful.
Scroll down & click "The Bible" link. mbsween.bike-night KZ750L3 page