The previous owners left 2 gas cans with fuel in them. Is there a way to tell if there are additives in them and if it is okay to use them in my mower (which has always used regular unleaded with no additives)? Would it harm the motor to use them anyway? The mower is a toro recycler with a briggs stratton engine.
Using old fuel that you are not sure of can be risky. With fuel prices being what they are I can see why you'd like to use it but I'd recommend that you mix it at 25% maximum with new fresh fuel that you have purchased. I'd also recommend that you add it through a fine filter screen just in case. As far as additives, unless it has been mixed for a 2-stroke engine, (chain saw / weed eater), there's not a good way to tell. Your best approach is to be suspicious and careful.
the previous owners left two cans of FUEL ! with maybe some brake fluid and bit of kero and whatever. you are meant to use fresh unleaded fuel or problems sure you can take the risk on stale fuel but could be somethine else then you buy a new lawnmower because you don't know what else is in that fuel they left it because they did not want a bar of it. don't use the gas and find out how to dispose of it correctly.
My concern would be moisture in the fuel and dirt that settles in the bottom of fuel containers. About the only hurting to the Briggs and Stratton motor would be gumming up the carburetor. The metal parts would be unaffected. You can try to use chamois cloth to clean the fuel as you are pouring into lawnmower. You might try some of the STP type of fuel additive that combines with the moisture to allow it to burn. Good luck.
