Thank you for your comment, and welcome. I finished this quad quite a while back, resolving most issues, and eventually sold it to focus on my Yamaha ATV. I really liked the Bearcat, but when the newer, bigger Yamaha deal fell in my lap, I decided to "thin the herd". Only thing I had a love hate felling about was the full time 4wd. It made it pull like a tractor when skidding small trees, etc., but it made it a little harder to steer, and was rough on the grass.
@FiReTHorN84 Thanks for the tip, but in the later videos I figured out the issues, and it ran well without an airbox for quite a while. I have since sold it.
Arctic cat had a recall on the carb, back in the day, and replaced the original carb with a new one. I missed the 'deadline' for a free replacement from Arctic Cat and it cost me $400 for the replacement carb many years ago. It ran way better with the new carb!
Most common cause of this is the float in the carb is not closing the inlet valve. Could be dirt or debris in the valve seat, or the float could sticking. You'll have to remove the carb, and try cleaning the associated parts.
you shouldn't use a wire wheel to clean spark plugs, it leaves metal deposits causing it to short out, use a blow torch, heat the electrode until it gets cherry red.