cold

I've noticed that when the engine is pretty cold it will 4 stroke a bit when cold but after it has warmed up there is no signs of 4 stroking at any throttle position. Is this normal? Does this happen because of some thermal expansion of the metal or something?

How is it to cold start those 66cc 2 stroke engines in between -0 and -20 celsius (35F to -4F)? Do i need to have the bicycle inside at winter? Do cold start harm the piston and cylinder badly? Do the piston easily freeze and stuck? Is it hard to coldstart?