I live in Alaska, we have to let them run with the choke on for almost five minutes as well. If you start to drive before it is warmed up fully, be gentle with it. It is ok to drive after say 2 minutes, just take it easy for a couple more minutes. I wouldn't even get on the throttle for at least 7-10 minutes. The risk you run if you get impatient and start to ride hard right out of the gate is, your piston and jug will expand and different rates and you end up scratching up your piston and jug. This is also known as a cold sieze. It definatly pays to be a little patient warming it up. A lot of guys up here like to bore their snowmacines and fourwheelers up here. We try to get the cast pistons when possible because your jug is cast. The forged piston is the most common though. Warming it up very good is really important here because it is a different kind of metal that expands at a totally different rate. They work great and are still very reiliable. You just have to be very careful to warm them up good before you ride them hard. Hope this helps.
Will