Based on your description of it chokes out only when warm - one of your coils could be near the end of its useful life. Sometimes they don’t act up when they’re cold, but they become weak and faulty once they get hot. Whats strange tho is, if your up to running temp, a weak coil would likely cause misfires all over the rpm range and not just high rpms. could be carb related

To determine if it’s carb related I’d do a plug reading. get it to a spot where u can open it up. Warm it up to temp, shut it down and swap the plugs with new. Start it back up, and immediately rip thru the gears, when you get to the choke point, pull clutch in and hit kill switch. Roll to a stop and pull the plug to see if it’s rich or lean condition.

Sounds like you just bought the quad with jetting already done? If so, i recomend pulling the carb and write down the jetting and needle clip position to figure out your current baseline. Fix the float needle while you got it out and give it a good cleaning. Is it running with airbox lid on/off? Does it run with choke on when warm? Only asking these questions because when I bought mine the previous owner had jetted the carb to compensate for incorrect float and needle position. As a result the quad ran like a complete pile of crap. Was all messed up.

Once you know the jetting that’s in it do a thorough read thru OMR carb mods and compare with what you got.

Hard to say without seeing run - could be a combo of a couple small things going on - incorrect float height, needle clip position height, etc etc. Plug reading, good carb cleaning, along with reading thru OMR carb writeup will get you moving in the right direction.