I'm working on my father's grass trimmer. Last time it ran was back in summer of 2017 and it ran good. After that it was abandoned and forgotten in my father's shed. I tried to revive the thing: replaced fulel filter, all fuel lines, rebuilt the carb, scrubbed the gas thank... After putting it together it started, ran for about 5 seconds and then gradually died out. I had a spare carb that came with the kit, quickly replaced it hoping for the improvement, but the thing would start, briefly respond to throttling up and down and then die out. Tried the new spark plug, no improvement. After it dies it's very hard to start it again. I'm running out of options. I ordered the crankcase gasket, maybe it'leaking and while waiting for it any suggestions what else I should check.