the OKOs' seem to differ a fair bit in jetting sizes too, depending if it is setup for a 2 stroke or a 4 stroke motor.
some of the 26mm OKOs i've seen come with a 95 main jet, and others with up to a 125 main jet, the latter obviously being for the 2 stroke bikes.
what pilot is your Koso running? im pretty sure my 24mm OKO Powerjet carb was supplied with a 50 pilot
i agree on the Koso being a better build quality too,
some i've seen have a polished, or at least a machined intake side, this gets rid of the lip where the intake bore steps down to the slide, creating less turbulence and a more atomised fuel/air mix.
another couple of things i found while tuning them
some of them can run a bit lean if you dont have a rubber boot where the throttle cable meets the adjuster on the top of the carby.
you can check this by running some insulation tape over the join and giving it another run.
if it runs a bit richer, then there is a vacuum leak there.
you can make it a more permanent fix by using the correct throttle cable boot, or by using some heat shrink tubing over the join to help it seal.
the mixture screw will need adjusting/resetting then too, once that problem has been sorted.
and finally with the carby problem of it not idling, that one is easy enough to solve too.
the genuine Keihin PJ carbys use a choke knob that is adjustable, the PWK choke knob isnt adjustable.
fit a Keihin PJ choke knob onto your OKO,
then turning the choke knob anticlockwise will richen the idle, and visa-versa, clockwise will lean the idle.
otherwise, just be happy with your MX style throttle, and keep having to blip it to keep the bike running.