Several things to check(basic tune up):
1. Proper sparkplugs(heat range) and correct gap.
2. Clean and inspect air filter(s).
3. Correct tire pressures.
4. Inspect/adjust chain tightness.
5. Check/adjust valve clearances.
6. Check compression in all 4 cylinders.
7. If possible, raise the wheels off the ground, and spin them looking for wheel bearing problems.
8. Inspect/adjust for dragging brakes.