Which KZ had a single frame member behind the carb air intakes?

This KZ400 has mismatching frame and engine. I'm trying to find an airbox that will reach around the frame member to the carbs. That probably means figuring-out what kind of KZ the frame came from. Anybody recognize this frame design? Note that behind the carbs, the frame has an upside-down "wishbone" design, with a single vertical tube right behind the carbs.

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FYI, the frame is stamped K4-067512. When I look that up, I find a reference to this:
- 398cc (K)Z400-D4 1977 K4E095101 K4-065101 Candy Super Red
...but the BikeBandit parts fiche for 1977 KZ400 shows two separate frame members behind the carbs... not a wishbone like this KZ.

Looks like a 1977 D4 to me.
www.partzilla.com/catalog/kawasaki/motor...fittings-76-77-kz400



www.kawasaki.com/Parts/PartsDiagram/142737/1977/KZ400-D4

Maybe I don't understand, but it seems like you're making this more complicated than needed. You didn't give the engine number, but from CycleChaos.com the K4-067512 frame number indicates that it's a 77 400-D4. Cyclechaos also has the engine numbers.

Assuming it's a D4, search for the airbox on EB or a motorcycle salvage yard. It may take a while to find a good complete airbox. It's kind of common for some of the parts to be missing, especially the cap. Partzilla has a cross-reference.

....

Based on the carbs and frame, it could be a 77 D4, 77 S3 or 78 A2. (As Texas and Martin said.)
Those are the CV32 carbs.
They use carb holder 16065-048.

All of the 77 frames use the backbone between the carbs.
So do all of the previous frames.
The perimeter frame did not happen until the 78 B1 and 78 C1.
(But the 78A2 still had the center backbone splitting the carbs.)

In that range, roughly 76 to 78, the airbox is the same for the piston-slide VB36 carbs as it is for the diaphragm CV 32carbs
but the boots are longer on the CV32 because the carbs are shorter.

The airbox and boots needed are:
Air box: 11010-1017
Boots for 77S3, 77D4, 78A2 : 11015-062

(Boots for the piston carbs on the same airbox for the 76D3, 76S2 : 11015-052)