During the time it refuses to start, get off and remove the spark plug and see if it's tip is wet with fuel. If it is, theres a chance that while the bike sits around, a slight leak drips into the crankcase. This puddle of fuel is thrown up into the combustion chamber when you try to start it. That fouls the plug until the extra fuel is finally pushed out of the exhaust.
A weak spark can contribute to hard starting. Give the entire ignition system a tune up.. New spark plug, properly gapped (small gaps foul more easily), clean the points and check the gap, and check the ignition timing.
A weak/failed condenser causes a weak spark but when they go, the bike is not only hard to start but it runs like crap at all speeds..