This may be a two-fold problem and require two individual posts, but lets try here.

I have an Ariens Roto Tiller, and I started it last week and after some cranking, cleaning of plug, it finally started. I was all prepared to start tilling, but decided to add gasoline to it in order to have more than enough. Now this gas was old about 4 months in the container, however the tiller started right up, but only ran for about 10 minutes and then just slowed down and stopped running, and I can't restart it, so could it be a gas problem, for example water in the gas, or is there something else I should be looking at.

Also please note the tiller was stored without gas stabilizer, and I imagine its too late for that now.

 

Check for spark and go from there. If it has spark, remove the carb bowl and see if it has water or trash/varnish in it. If so, clean it out. You might have to clean the holes in the bolt that holds the carb bowl on as well.

 

If i where you i would drain the old gas from the tank and then give the carb a good cleaning that should solve any problems.