I've got two words for you: Solo Seat!
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I dislike taking passengers.
That said, I've ridden 2-up on a few different 400cc Hondas over the years (one a '70's 400-4 many moons ago, and the other my beloved CB-1)
It's doable. And my passengers have always had at least 50lbs on me....
I know it's already been written here, but to re-emphasize... Braking will take longer. Over-estimate until you are comfortable with it!
If your passenger has never been on a bike before have a little chat with them before ya'll get on the bike:
Remind them to lean with you, not opposite you. Ask them to please not wiggle around too much (I had a passenger once who was so twitchy the bike was handling with difficulty. grr.)
yeah.
But still... Solo Seat.