Good, clean fuel is the key to an easy starting lawnmower. Always use fresh fuel that has been stored for less than three months when topping up the tank, as most unleaded petrol will go stale after this time and, if used, will make the engine difficult to start. Always store fuel in a sealed container away from light and heat.
Using a good fuel additive will help to keep fuel fresh, add every time you add fresh fuel. It will also keep the carburettor clean for easy starting. Additionally a good additive will also protect against the corrosive effects of ethanol found in most fuel.
Please note: avoid using old metal cans to store fuel as these can rust on the inside and cause carburettor blockage.