1978 KZ1000A Front Master Cylinder for single disc

I have a 1978 KZ 1000 A with a single disc caliper.

Evidently Kawasaki installed a number of different master cylinders on their late 70's bikes.

My master cylinder needs replaced, but everything I am finding is for dual disc systems.

As I understand it there is a 5/8 version for dual discs, and a 14mm version for single discs.

I considered a rebuild kit, but as you can see from the photos, my mirror post is busted up, and I have also read that these plastic reservoirs are problematic.

Does anyone have a line on a single disc 14 mm master cylinder replacement, or a dual caliper upgrade kit option?

Does a dual disc upgrade require new brake-lines?

No eBay APP ID and/or Cert ID defined in Kunena configurationThis ad looks like a nice master, but it is indicating that it is a 14mm dual disc MC.

Ebay is full of 14mm masters for dirt cheap.

Regarding the lines, yes you should replace them. Not because they won't fit, but because they are sure to be full of sludge which builds up over 35 years.

You stated "As I understand it there is a 5/8 version for dual discs, and a 14mm version for single discs." That is true, so if the eBay seller is saying he has a 14mm master cylinder for dual disks; he is wrong.

If you switch to dual disks you're going to need to add a line and change the splitter (or make some other mod) to feed both calipers. So while you have the brake lines off you may as well replace them just to be safe. My bike has all the original brake lines and they have not given me any problems (here's where I knock on wood), but i have owned the bike since new, I park it in my garage out of the weather and sunlight, and I flush the brake fluid every two years, so that may help the health of the lines. Nonetheless, if I ever have them off for any reason I will replace them. Ed

Here is what the EBAY seller wrote back:
Yes, this will work GREAT on a single brake disc, this is a 14mm piston bore size, will work as well on a double disk SINGLE PISTON system, wont work on a doulbe disk twin piston system.

Right. Keep in mind that his primary goal is to sell the master cylinder, so like many eBay seller he would not hesitate to exaggerate. I recommend you get the correct master cylinder: 5/8" if you are installing dual disks; 14mm if you are installing a single disk. There is a reason Kawasaki and other manufacturers made the 2 different sizes. Ed

Nessism told me that the EX650s and 650 Ninja master cylinders will work and even have the treaded mirror hole in a post on page 1