Make sure you check/change the powerhead oil before trying to start it.
As advised by jezza2011 above, a drop of lube in the cylinder(s) won't go amiss.
Turn it over slowly with the plugs out, then again with the plugs in, to make sure the valves aren't stuck open.
When priming fresh fuel through, check the carb for leaks, as gaskets and seals dry out and shrink if they haven't seen fuel for a few years.
If/when it starts, let it run at idle for a while to warm up before opening the throttle to any degree.
If all ok, do the full service, as advised by willk/Nos.
Fitting a killswitch should be a doddle.