If you've never used Sea Foam motor additive, it is an engine owner's best friend. For small engines like those in lawn mowers or other gas-powered yard equipment, it is great to have. Add it to your gas tank to help reduce varnish and stabilize the gas; add it to your oil to help clean the engine and keep the insides running good. It works in 2-cycle engines, 4-cycle engines, and diesel engines.
Sea Foam typically sells for around $10 for a 16 ounce can. On Amazon.com right now it's listed for $7.47 (eligible for free shipping) so it's a great time to stock up on a few cans. I think that's the lowest price at which I've ever seen it sold.