+1. I've had a Suz, a Yam & my current Merc all do the same thing.
To test - forget priming - I assume you are on electric "remote control" choke? - (If not you need a fast fingered volunteer by the engine!)
When it starts to go funny - just blip the choke - and I mean literlaly tap the button / twitch the switch - if it then takes off like a scalded cat as you relese the switch your idle mix is just slightly too lean. Ipve never had to move the adjusrer more than 1/8 of a turn from the "manual's going in point "
I can't rmember if I read you had changed prop - my Merc did that after I went from a 13" to 14" pitch - the extra load was enough to tip it over the edge, and like you it was fine when stone cold.