valves need to adjusted, can not find valve covers on engine.

I have replaced the selinoid and checked the battery and the battery is good. I can get the mower to crank over just fine with one of the spark plugs out and as soon as I shut it off it acts like the battery is dead. I have done some research on line and it states to adjust the valves, however I can not fine the valve covers on the engine. Do I have to take the heads off in order to get to the valves to adjust them?