Stock setting on the needle and a 270 main?? You sure your mid range is OK?? Do the revs hang? Anyways, I ride in the winter (when the snow isn't too deep) and I go up two to three sizes on the main jet, keep the pilot the same, and sometimes play with the needle depending on how it's running.
The next big thing after jetting is using good fuel and the correct mixture. I always get exactly one gallon from the pump and pre-mix using a ratio-rite. Dont' add extra oil to the premix as this will lean you out!! Use the highest octane you can get.
When it's really cold out you'll want to warm the engine a bit before just beating on it. I recommend revving it a bit while letting it warm, not just letting it sit at idle and collect oil in the crankcase! Once it's warm and running without choke, putt around and see how it feels. If it's pinging or sticking, adjust the jetting. Make sure you've got the jetting right before you go tooling around and beating on it or your motor won't be happy. If you're not seeing any smoke out of the tailpipe at all, check your jetting!
Also, you may want to get some screw in studs for the tires!
