2007 Kfx700 can't get it tuned right
 

2007 Kfx700, been so long ago I don't know exactly how it started but I just can't get my atv to run as good as it should, and use to run.
Basically it started being very hard starting and just not running/idling well. I did my first ever valve adjustment and I was so happy because it started right up and idled perfect with lots of power! She was back! But it only lasted about 5 minutes. Once she warms up starts running really rich, black smoke out the tail pipe, low idle, sometimes dies after being on the throttle.

I've had 2 shops look at this thing the past year and they've replaced the choke cable, fuel petcock, adjusted the valves again, new vacuum valves in the carb, new float valves, new spark plugs and $2k later its exactly the same!! :(:(
I've cleaned the carbs multiple times, I have a freshly cleaned and oiled k&n air filter in even with the air fuel mixture screws turned all the way in, she's running very rich on idle and low throttle, black smoke puffs every time I Rev it.

Please help, what am I missing!? Do the carbs have to be synced? Does it sound electrical like cdi box or coil? Timing?

Hard starting after being ridden and engine is hot. After she cools it starts easy and idles good for a bit.

You might have to rejet it for the k&n air filter or you might have bad rings and it's burning oil witch would blow out black smoke, try doing a compression test. And tell me what you get