Running poor, assuming spun timing gear

Scrambler 850, Hard to start, have to give it a little throttle. Lacking power. Idle is around 1000-1100. Changed plugs. no difference.

What are some things to check before pulling the valve cover to check timing?

Just had motor out of it a few weeks back. Rode 40 miles or so, ran great.

Went to ride last night and ran like shit from the start.