Hi Jakes, Thought I'd comment on my experience with a Shindy kit. I have a 1986 Kawasaki Bayou 300 owned since new. Good machine, weak points in my opinion are the carburetor and starter. Keihin CVK-32 vaccuum slide carb very picky about dirt. Ever so often it won't start, I drain the float bowl helps it fire up (water?), then if it persists it's carb clean time. Probably done it a dozen times now, do it in my sleep.
Anyway, I decided at one point about 2014 to put in a new carb kit, since it still had all the original seals and jets from near 30 years before. Like you I bought a Shindy kit, feeling they were good quality and Japanese for a Japanese ATV.
Well, from the get go I had a high unstable idle - either racing or died. I'm not sure, the tiny washer on the pilot screw might have been bent. Anyway, I put back in the original pilot screw and problem gone. Further update, for a number of reasons I won't go into here, the machine sat from 2017 until 2020, wasn't started at all. Needless to say I cleaned the carb, upon disassembly I found the Shindy float bowl o-ring had turned to gooey TAR. So, in absence of anything else I put back and am currently using the original OEM float bowl o-ring, jets and parts from 1986, and it is running great. Just needs a bit of ether if it goes much below freezing, getting old. Starts instantly and idles smooth otherwise, see a video on how it starts and my starter motor replace tip below:
https://www.youtube.com/watch?v=h1rUehPXoaY
So draw your own conclusion. Hope you find that interesting if nothing else. I'm currently helping another fellow with a 1993 Suzuki QuadRunner 300, he bought a Chinese carb for it as the original carb was 'lost' (??), so I have no baseline to compare with. With my experience with my Kawasaki, and like you cleaning all 3 of yours, I'm sure I could have gotten it running perfect by simply cleaning the old carb, but what is to be will be...:o) Am getting close to it running decent.
Try putting back in your original OEM parts in one of your OEM carbs and try that - what have you got to lose?....:o)
Cheers Jakes!~ Bellarmine