My macculoch 210 strimmer (petrol) will not start/?

I have checked: filter, washed out petrpl tank, checked brass filter in cap. There is clearly a blockage somewhere. The most noticeable thing is that when trying to prime the carb the plastic primer remained dented and does not resume its domed shape. If I loosen one of the screws holding the plastic primer in place - there is a hissing sound of air rushing somewhere. Primer cap gets back to its normal shape. However next try , no fuel goes to carb. I had the engine running for a few seconds but it did not continue. Electrical side seems OK. Have you had anything like this in your experience. Help appreciated.
Mike