A pal in Pittsburgh who builds bikes I bought one of his over a few years ago swears by it interesting to hear any other thoughts but this is what the blurb on eBay says about the one he uses and I have bought ‘Use STA-BIL Fuel Stabilizer in any gasoline-powered vehicle or equipment you plan to store for 30-days or longer. It keeps the fuel fresh for up to 24 months during storage, eliminating the need to drain your tank. Works effectively in all gasoline blends, including Ethanol-blended fuel, up to E-85. 1-ounce (30-milliliter) treats up to 2½ gallons (9.5-liters) of fuel. Use STA-BIL only with fresh fuel, and keep gas can or tank 95% full to avoid condensation build up in tank during storage. Run Engine for 5 minutes after adding product to treat entire fuel system. Product does not contain alcohol. Perfect for collector cars, generators, lawn mowers, snow blowers, etc.’ cost about £12 to me.