Fill all fuel tanks and add fuel stabilizer (Sta-Bil, 1oz(30mL) to every 2.5 gallons(9.5L) 
(0.4oz per gallon) which is equivalent to  3.6mL per Litre:
Tractor Sears Craftsman Model #: 944.607860, 24.0 HP 46" Mower> Gas Tank Capacity: 3 gallons (1-1/4oz stabilizer) Push Mower Mastercraft Model #: C459-36203 Gas Tank Capacity: 1.6US Quarts(1.5L) add 5.4mL or 0.18oz stabilizer Husqvarna Model 128LD Gas Trimmer Gas Tank Capacity: 13.53 US Fluid Ounces = 0.4L add 0.1oz stabilizer
Old Trimmer: Husqvarna Model 325L Gas Trimmer Gas Tank Capacity: 0.343L=0.075 gallons = 0.1oz stabilizer