Fuck all the pissing about and go to your local bike shop and get a new plug. This will more than likely be the problem i get it all the time with my crosser so keep a spare wi me when i go out on it. also put in freash petrol and 2 stroke. as for checking the most commom colour for 2 stroke is red or blue.

Check the commpression take the plug out n put ur thumb over the top and pull the cord it should force ur thumb off.