Beerbelly - Perfectly normal with the Mariner as noted above due to 'stat.
Better the devil you know but all engines have issues regardless of make.
Anyway, to finish off the post earlier this evening with the pic, once I had the carb off I blew through all the orifices and jets and cleaned up the gunky plunger so it moved freely again.
And...bingo! It started on idle once more. Not sure what the plunger thing actually does but something to do with flow from the float bowl?!? I'm pretty sure that was the issue rather than a blocked jet?
However, on disassembling I mistakenly moved the mixture screw setting so need a little more help!
Can anyone give me a layman's guide/ballpark to setting this mixture screw correctly on the Mariner and an idle setting as all the workshop manual figures are for an engine in gear on the water...?
And I did not note which way up the float should go in the bowl. One side has a slightly raised concentric ring that I guessed should go against the brass float pin thingy rather than against the base of the bowl?