This is my second Z with a FR651V, & I always start mine with low speed throttle position. & maybe 3/4 choke for a mili second.
Actually I use one hand for the key, & other on choke knob. Second it fires get the choke off Fully..
Mine starts instantly. And I let it run slow for a few like the Owners Manual states.. & shut it down same way..
Low speed. Also engage blades after warm up at just a bit higher RPM, then when engaged take rpm's up to full..
Much easier on the blades clutch. Also stated in the Kawasaki owners manual.