I have written on this forum of my experience with Sta-Bil. In essence, I didn't use it for a period of nearly twenty years, and had no fuel-related problems at all. I have been using it for the last five or six years, and have had no fuel-related problems. The only difference I can detect is the smell of the exhaust, and the slight coloration of the fuel with Sta-Bil added. However, it is the only additive mentioned by name in the owner's manuals for Kawasaki, Suzuki, and Craftsman. Except for Sta-Bil, those manuals say fuel (and oil) additives are not necessary and will do nothing except increase costs.

I have been unable to find out what is in Sta-Bil. The MSDS sheets available on the Web seem to come up with about 95% "Heavy Aromatic Naphtha (Solvent Naphtha)" and 5% Naphthalene, which is the ingredient in mothballs. They also mention something about proprietary ingredients, or manufacturer's secret formula, which is permissible in an MSDS if the hazards and precautions are properly spelled out. I point out that, if any of you run a business, and use Sta-Bil in the course of that business, you are required to have the MSDS on hand and available to your employees. Perhaps that MSDS will have more information.