If the bike has done some caughing or poping when trying to start yes it could be that the flywheel timing has slipped. Maybe the PO had the flywheel off and it was not cranked down tight enough.
You can check a rough estimate of the timing by just removing the spark plug and then use a small screwdriver to feel for the top of the piston. When the piston is at the very top of the stroke then glance at the rubber grommet that holds the spark plug cable and you will see the arrow line will be about 3/4 if an inch to the right of the center of the rubber grommet.
If its like roughly in that area give or take a 1/4" it will start. If it's 2-3" on either side your timing has slipped