2014 Sportsman XP 850HO jerking from a stop

Hi all. New to the forum and new to ATV troubleshooting.

I have a ’14 Sportsman XP 850 HP with low miles and low hours. But it was ridden HARD (mud, water, alcohol, etc…) by my son.

The ATV jerks when applying throttle from a stop. I get up to about 1900 RPM before the clutch will engage. When it does engage, the ATV bucks and jerks. Once I get the clutch to engage. It seems to accelerate well.

I have some understanding of the workings of centrifugal clutches. Get to a certain RPM and the plates close on the drive clutch and open on the driven clutch.

I had the clutch cover off and nothing seemed to be broken and the belt was not frayed or missing teeth.

Where do I start?

Thanks in advance.