When you say another hole, you mean there were 5 holes drilled in the slide? What is butterflies? Do you have a photo of the slides to ZR-7?There is a forum The Zephyr Zone • Index page. It is Brit, but there is not much action because is restricted to Zephyrs, and not many were sold.
Interesting,...... when you started this thread, asking about the holes on the slides, I was one of the ones who responded in the US there is no holes. That was true on the Zephyr, however, recently I discovered that the ZR-7 carbs, the successor to the Zephyr in North America, had the slides showing another hole facing the butterflies. I tried them on the Zephyr, but could not see much difference really. To me the extra holes should, theoretically, moves the slides more briskly.
When I searched information for the restricted european zephyres, I found on other kawasaki forum that was dedicated to popular one kind of model with one piston/carb adventure bike. Where they told that holes were drilled to make sure that the slides would not be able to lift all the way up, in that way, restricting the flow. Plugging them, would make sure that the slides would lift all the way up. However, in my case, I plugged all holes as I showed to you, because you all helped me to find information that Zephyre slides DID in fact not come with drilled hole at all.