It is best to fill the gas tank and in order from best to acceptable is race gas, aviation low lead 100 and then non oxygenated gas. Add a stabilizer; Startron, Sea foam and then Stabil. Warm bike well and then change oil, warming bike well will not allow contaminates (sulfur,H20,etc) to end up in your engine,exhaust system. Drain all fuel from carburetors. Here are a few ways , turn off petcock if it is not a vacuum unit and then ride/run until engine dies ,restart with choke until it will not run anymore, then drain float bowls if possible. For Vacuum petcocks it is best to drain bowls otherwise you can pinch off fuel line or remove and cap vac line(or pinch vac line) and run until it stalls. Some petcocks will bypass through the long winter storage so one of the best ways to stop any fuel from ending up in the carburetor is to remove the fuel hose from the petcock and cap/plug the petcock and fuel hose. Remove your battery and trickle charge every month or keep it on a tender. If you have a center stand use it to remove weight from tires, It is also a good time to lube all pivots and cables. These tips will keep you from having start up and carburetor problems in the spring…Good luck.