This section discusses what to check with your fuel.
As gasoline ages, the way it smells changes. I don’t particularily like the smell of gasoline, but old gasoline smells even worse. Most gasoline now contains a certain percentage of alcohol. Since alcohol tends to absorb moisture current gasoline tends to deteriorate rather rapidly. There are several additives that you can put in gasoline to slow down the aging process. I add MMO (Marvel Mystery Oil) to all my gasoline since it also seems to prevent a variety of problems such as sticking valves. But I’m sure any automotive supply shop can recommend something that will work for you.
I would recommend that you remove the gas tank to make sure that you’ve removed all the old gasoline. If the gasoline has gotten so old that it’s in the “gummy” stage, you’ll have use some sort of chemical cleaning process. Muriatic acid will work for this but must be used with extreme care and don’t use it if you’re not used to dealing with it. The fumes can kill you. Rather than take a chance with something you don’t know how to deal with, I’d suggest you check with your local automotive supply shop for a recommendation.