A lot of people think that starting an engine every week or month is going to keep their engines in good shape. This is completly wrong.
Pitbull is right regarding moisture buil up if you don't let it warm up completly and some engines will never reach normal operating temps just idling, especially if the ambient temp is cold.
Wifes Corolla for instance won't hit normal temps until driven several miles even if left idling for 30 minutes ( something we do up north to deice the car ).
Once you shut off the engine all the oil coating the internals starts to run down to the sump, my info says that in about three to four days the oil has completely run off the parts and that starting it then would cause the equivalent of 500 miles of wear until the oil recoats the parts. Staring it once every month for 6 months would cause 3,000 miles of wear on the engine and every week would come out to 2,000 miles per month or 12,000 miles of wear in a six month period.
Sparkplugs provide spark to ignite the fuel, but they too must reach optimum temps to completely burn off oil and fuel residue if not fouling is pretty much garanteed. Two stroke dirtbikes owners can ruin a plug by fouling everytime out in some cases if they don't ride them hard enough or use a plug that's HOT enough.
Best bet is to leave well enough alone until you are ready to ride it regularly. When starting it for the first time of the season, pull the plugs and check them. If they look okay then they probably are, but then again they're not that expensive so why not play it safe. I cut the fuel to the carbs and turn the engine over with the plugs out a couple of times in order to try and recoat the internals with oil ( it is best to ground the plugs to the engine when doing this, especially with fuel injected bikes ), I then reinstall the plugs which gives the oil a chance to run a little on the parts then open the fuel and fire it up.
BTW oil does get thicker as it gets colder but temps of around 30 degrees f shouldn't make it thick enough to hamper engine startup, believe me I know about operating engines in the cold. Testing the plugs on engine block shouldn't hurt anything.
I know that this will seem obvious but...... Did you check that you still have gas in the tank, I had a defective vent cap on a snowmobile and although I had stored it with a full tank with stabiliser, after trying to start it for several hours my wife says to me "Is there any gas in it" of course there is I answer all bothered by her comment, as I take the cap off to prove that I'm not an idiot, I am hit with the realisation that all the fuel had evaporated.
