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Discussion Starter · #1 ·
I had just completed my top-end rebuild on my 90 zx-11c, and started her up for the first time since I have owned her. It ran, but rough so I pulled apart the carbs (had expected to anyway) I found two of the vacuum valve bags were torn. Kawi wants about $87 each for the bags. (There must be $2 worth of materials there) So I bought a set of carbs on ebay for $100. The seller claims they were from a 92 zx-11. He also gave the engine #ZXT10CE030066, which as best I can tell is from the non-US model-ZZR. Anyway, (and I can't confirm because they haven't arrived yet) The seller claims the main jets are 148s. Stock jets for the 92 are 140s (I am not sure what is stock for non US models) My 90 uses 155 jets which I have currently and could re-use in the new carbs.

So my question is, Why did Kawasaki change to a smaller jet in 92? As far as I can tell the ram air tube is the same. Was it a mis-calculation for 1990, and the jet's should have been smaller? And finally, should I use the 148 jets coming with the new carbs or swap with my 155s.

I am new here to the forum and have been eating up the existing posts. There is a wealth of knowledge here. Keep up the good work!
 

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In about 1991½, Kawasaki changed MJ size from 155 to 140 (like you already figured out). At the same time, they added a short (~80mm) extension on the tube that pressurize the carb's bowls. This extension is at the "nose" of the ram-air and comes with a mandatory curved grill (previous one was flat).

Yours being a 1990 is using 155 MJ. When you receive your "new" carbs, you must install 155 MJ inside them. It is not a miscalculation Kawasaki made. They made this change to eliminate an hesitation in the carbs in a particular condition with side winds.

All those MJ numbers are OEM Keihin. Do not mix those numbers with MJ coming from Dynajet as they do not flow the same. FWIW, Factory Pro jet kits also use OEM Keihin MJ.
 

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Discussion Starter · #3 ·
So, if I understand you correctly, the higher bowl pressure of the '92 allows more fuel to travel through the smaller jet?

I'll use the 155s as you advise but I am curious what size Factory Pro would recommend for the '90 (I haven't done any research so excuse me if the answer has been discussed, or is two clicks away on Google)

Thanks for the help!
 
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