I would start by turning in the air screws 1/4 turn and testing. If you turn the air screws in and out and nothing changes, then the pilot jets and passages need to be cleaned. It's VERY common to get small varnish buildup in those, even after cleaning.
When you have the carb out, take a strand of monofilament fishing line and put it through the pilot jet; you will sometimes be amazed at how much stuff is left in the pilot jet even after soaking in carb cleaner. I have also used a strand of telephone line, but there is a chance that the copper can scratch the jet.. have to be careful.
I have the pilots on my 650 one turn out from lightly seated, there is NO hesitation or bog on takeoff.
If that doesn't help, then turn to the clutch...