Thank you all for your suggestions! After going through the advice on the forum, I decided to check the spark plugs. When I pulled them out, they were covered in black, sooty carbon deposits and seemed a bit wet, which pointed to fuel flooding.

It became clear that the plugs were fouled, likely from a rich fuel mixture or incomplete combustion. I swapped out the old plugs for new ones, cleaned the ignition coil terminals, and checked the spark plug wires.

With the new plugs installed, the engine started right up and ran smoothly. It turns out the fouling was the main issue, and thanks to the forum’s advice, I was able to get my Sportsman 800 running perfectly again.

I really appreciate the help from everyone—it made a huge difference in getting my ATV back in great shape!