Small Engines (Lawn Mowers, etc.): Briggs 16 hp OHV, valve clearances, valve clearance

Question
I have a Craftsman tractor with a Briggs 16 hp OHV engine. From day one it's been hard to start. Won't turn over fast enough. I have replaced the battery, starter and solenoid several times. I also researched the problem and discovered that valve clearance could be an issue. I then adjusted the valve clearances to .004 intake and .006 exhaust. Is there anything else I could try? It still turns over hard. Sometimes it won't start and if you try it again 30 min. later it will turn over fast enough to start. I hope you can help me. I'm at my wits end.

Answer
Grounds, grounds, grounds.

Remove every ground wire you can find and clean thourougly.  See what happens.  We have to start here first.  Don't forget, the engine probably grounds through  the engine mounting bolts.  Remove and clean at least one of these.