Gunna be a tuning issue more than likely.
But i would start with the easy stuff first.
New plug gapped right
Clean the airfilter
Drain gas and refill with fresh.
Start there and see if the problem goes away.
Also if there are any mods make sure to tell us all of them. And if its been jetted for the mods again give us as much info as possible.
If the quad has sat for even a year its possible the carb could be dirty and require a good cleaning.
To many mods to list in signature(ran out of space lol)
Check out garage for full list