Thanks folks, just had a bit of a go at it but not much time... The filter bowl was full of gunk but too tricky to remove today - will give it a clean out. I tried directly connecting the fuel lines to a plastic jerry can of diesel and it did seem to start a bit easier but then faded again after a few bangs. However, I suspect there is gunk elsewhere in the fuel system given there is no filter element and the filter bowl is full of gunk.