Be sure you get all of the leftover fuel out of the engine. I feel that it is the presence of methanol more than the absence of oil that rusts engine parts. I like to attach an aquarium air pump to the muffler pressure tap and plug the exhaust outlet. Then I find a crank position where all the ports are open and let the air purge out all remnants of unburned fuel that may still be in the engine. The air enters the exhaust port and exits through the carburator. On my four strokes, I attach the air pump to the crankcase vent and the air escapes through the front bearings and past the piston ring.