You're in good hands mate with these guys, they helped me out a lot with my carb issues too. I had a similar situation with my KLR (single cylinder) - really rough idle and a black plug - huge plumes of black exhaust when I blipped the throttle. Took the carb apart, checked the float valve wasn't sticking and made sure the float height was correct, and pulled all the aftermarket needles, jets from the carb and replaced it with stock. Still have some work to do on it but just wanted to say that I'm no pro - once I got my head around a little how the carb works it really helped me understand what was wrong. You got this.