This time I’m tackling the Z-series original carburettor VM, which I’m really not good with. It’s not particularly unusual in structure, but there are just too many types of this VM carburettor.
And so much time has passed that it takes forever to verify whether that carburettor is original or a mix-and-match. First I check the manual, confirm the actual part, then order components—that’s the flow.
Found the KZ900 service manual on “Internet Archive“.
I couldn’t find the KZ900 anywhere on the service manual sites I know, so I searched all over the internet and finally found it. “Internet Archive” ← This jumps straight to the KZ900 page. Some pages require you to create an ID and log in to view. Note that you can’t view the KZ900 without creating an ID. *You can’t download anything related to the KZ900.
For better or worse, this is how we accumulate all sorts of mysterious information through work research, both me and everyone else.
Apparently there are three types: VM26SS, VM28SS, and VM28SC?
This VM carburettor looks similar but comes in so many varieties that it’s kind of a pain. They exist in various forms depending on the specification and year, so you order parts and they don’t fit. That happens pretty often.
The carburettor bore diameter is different, so the body size varies slightly—it’s quite deep.
And the inlet diameter on the carburettor side is also a quirk. You’d hope that if it’s 26φ it would be exactly 26.0, but it’s something like 26.73~, which is incredibly precise. 27? 26.7? When you really think about it, your head starts to hurt.
Unlike other VM carburettors, this one has a different linkage setup—it’s a bit special. Without a service manual, there’s no way to handle this. You need to know the jet numbers and needle inside, and you need to know the actual fuel level height.
Having a service manual makes all the difference in peace of mind.
First, let’s remove the carburettor currently in use and check it.
For now, the carburettor is still running, so the condition is reassuring. However, it apparently has a history of disassembly and the internals are unknown, which is why we’re checking it this time.
We made a promise not to disassemble the four-stack because it gets too complicated. *This kind of forced opening and closing sometimes breaks or snaps off during work, and you end up having to hunt for replacement parts—a real rabbit hole that I’d rather avoid.
For now, I’ve finished the top and float chamber with wet blasting.
*The image is a parts donor. The working carburettor had a somewhat questionable finish overall. I always think about this, but motorcycles really do run no matter what condition they’re in. It’s amazing.
The jets inside seem to have been replaced with reproduction ones.
They also prepared a parts donor, so let’s check it.
It’s absolutely terrible. A huge amount of mysterious white powder came out, and I was pretty shocked.
Plus the throttle valve screw threads were stripped, so it was a real pain to remove.
I wet-blasted the jets to clean them up since the numbers were unreadable. I’ve already ordered O-rings and gaskets.
I want to measure the needle and think about which one to use.
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