Hi,my petrol strimmer has broken down.It appears to be a fuel problem.The make is dynamac.?

I have checked the filter and fuel lines and they seem to be ok.The bulb for priming the engine is in good nick but when i press it a couple of times it stays hard and will not pump the petrol from the tank to the carb.I have taken the spark plug out and injected a little fuel into the engine and it fires up first time.I am now at a loss as to what to do next.Hope someone out there can help.Thanks in anticipation.Dave.