If all the above suggestions fail, I might try starting fluid instead of fuel/oil mix in carb. Had an evinrude from the 60s that would only start that way, but started reliably at that.
Lastly, carb overhauls and adjustments almost require an artisan's hand to get right. I'm pretty handy with a wrench, but punt that job to a shop. Saves a lot of headache.
good luck, and always remember, its an inanimate object....not a living being determined to taunt and frustrate you with superhuman powers.