One thing that can cause hard starting with an engine like that is if it loses valve clearance (valve lash). The valve seats wear faster than the valve train, so over time, the engine loses the slack which allows the valves to close properly. When that happens, the valves start to leak, which makes the engine hard to start. I believe the correct setting for those engines is 0.004 inch intake / 0.006 inch exhaust, set cold.