Aldo, you are probably aware of this but a lot of chainsaws, trimmers etc. are prone to starting problems due to the system that allows air into the fuel tank, to replace the fuel pumped out, not working. You can diagnose the problem by checking whether it will start and continue to run when you loosen the cap, but not otherwise. Most models have either a squashed tube or a flap valve built into the petrol tank cap, to allow the air in. When the machine is left laying around for a long time the oil oxidises in this tank cap vent, and the oxidised oil glues the valve shut. If that happens you need to wash the vent in petrol to clean it, after which it will be as good as new.
