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Right now I have a set of 26 mm carbs (1976) on the KZ1000. They are stock jetting. My original 28 mm with accelerator pump are also stock jetting, but I took them off to clean them and have not yet put them back on. Both my Z1B's are stock jetting with stock air intake and exhaust.

It sounds like your main jets are not the problem. Main jets are not the fuel source at lower rpm's. There isn't enough vacum differential to pull fuel up the mains until you reach about 1/4 throttle. They provide no fuel at startup...better to use your choke with no throttle to start.


You should look at your needle settings and maybe enrich (raise) them by one clip position. This will allow more fuel through the needle jet at higher rpm's....say up to about 3/4 throttle. Needles control fuel flow from the main jets up to that point. From 3/4 throttle onwards it's the size of the mains that controls the amount of fuel. You could also experiment with larger pilot jets if your issue is at low rpm's. You should also look at your fuel screw settings and perhaps richen them up a bit for better low end performance.

Edited to add that 150 mains are huge compared to stock 112.5 mains. Waay too big IMO.

I'm think I'll book some dyno time at a shop nearby, in the near future
(Atm I'm working on my Pan European (my everyday bike). that needs a bit of care as well , so that's my first priority.. )
The weird thing is , no smoke on startup. and starting is still really easy. a bit of choke, one kick. ?Bingo she runs .