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Good to know ! I am only using Keihin jets so it should'nt be a problem.

I am still curious to know why you suggest to use an entire DynoJet kit instead of just going down a few sizes with my main jet ? Is there a trick I should know about ?
Because at $100+, the kit is quite expensive...

Try the correct factory jets and if it cleans up the plugs fine.
If not get the jet kit, it contains more than just jets, like jet needles, springs etc...


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Will do !
One last thing, I have a spare set of CV34 from a KZ750.
Would it make sense to swap the CV36 for these ? Would it get closer in terms of specs to the original VB32 of the KZ400 B2 ?

 

No, 2mm is not that much of a difference


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Just wanted to post an update on that topic.
I found myself a set of CV32 keihin carbs, stock for both the KZ400H and the KZ400 B, which I installed on my KZ (the airbox is the 400H one, as I have a KZ400 B engine in a KZ440 frame - the KZ400H airbox is the same as the KZ440).
The bike now runs great !
I just had a slight blip off idle, with the engine stuttering when I started opening the throttle but after adjusting the float level, it is now perfect through all ranges.
Another problem I encountered that could be of help to others is that when I first installed the new carbs on the engine, it acted as if there was an air leak. When setting the idle, I couldn't bring the idle back down, even by closing completely the idle screw. Turns out one of the butterfly was bent and letting fuel in even with throttle and idle screw closed. So if you encounter that problem and can't find an air leak, could be this !