You'll likely get allot of different suggestions of things to use, some are hard to find and might even have to be ordered, so I use what is easily available found on the shelf, Lucas gas/diesel fuel injector cleaner additive, I just get the small bottle, although it states it can treat 25 gal. I find it easier just to use half a bottle at each 2 tanks fills, it s seems to keep the engine running good and smooth, quites it down some as well,