you can store with gas but, it is better for the engine to store without also never store a diesel engine with gas in it cus diesel fuel gums up in the winter.

I would drain out or use up the gasoline in the tank before storing it for the winter. Gasoline can start to decline in performance as it gets older.

Also is a good time to change out the oil and check the spark plugs and battery terminals .

im pretty sure it doesnt matter

You can store with or without gas. However, you should store your lawn mower in a building. If you don’t have a storage building, cover the mower with a tarp and put it under a shelter. To keep the battery charged during the winter months, once every two weeks, crank the mower and leave in on for approximately 10 minutes.

Lawn tractor storage for winter…
suggest leaving battery, charged and connected to help prevent rust,
gas , either refresh or keep some near by, just in case of some odd emergency, lubricate and grease per manual or instructions,
cover with tarp, with some ventilation,
check oil is topped up or drain and refresh now or in spring,
check plugs and wires, if needed….

http://www.contentmart.com/ContentMart/content.asp?LinkID=19764&CatID=328&content=1

http://abbysguide.com/lawn-mower/content/lawnmowerwinterstoragetips_158.html

Store ours without gas. Also remove blade for sharpening.

I’ve always stored with a full tank of gas, to eliminate condensation in the tank. The last few years we would add Sta-bil or Seafoam, because the gas is so crappy now. Add the fuel stabilizer and run for 5 minutes. Shut off the gas valve.

I always leave gas in em….. leave it full to minimize condensation, put tinfoil over the gas cap….
Use a fuel stabilizer (like stabil, or briggs brand, or seafoam are good ones)
I have never taken the battery out, or started the mowers every once in a while, and they do fine…. but you may want to take the battery out and keep it on a battery tender in a try place….
In a shed is best….. if under a tarp. make sure to put a tarp under the mower!!! condensation comes from the ground, and will get trapped by a tarp!!

Change the oil of course and air filter….