You need to verify that the slide is positioned correctly for it to idle and so the idle mixture screw will operate as it should. look at this link it shows some of the basics but not the slide height. you need to verify that when the throttle is closed that there is a bit of cable slack so the carb slide is all the way down. Mikuni Carburetor Tuning – Affordable Go Karts I have to go out but I will see if there are any good videos for you to watch. I looked on youtube but the ones I saw were not good. You need to understand the 4 stages of tuning for this carb. Right now we are just trying to get the 1 stage working which is the idle with throttle closed and running on the enrichment on setting. The problem is GPS had their hands on it then you got it and it did not work and you adjusted stuff some more so we need to start from ground zero. You have verified the engine starts on starting fluid so other than a air leak it sure looks like the carb is the issue. Keep in mind we are not there with you so we have to go with the test results you provide.
thank you for being such a big help through all of this