Kz650 choke issue

The details:
81 csr 650
Cheap pods
4-1 kirker
77 or 78 carbs "non pumper"

Rebuilt this 650 and parts were missing from original carbs. Rebuilt a set of carbs from another bike. Carbs ultra sonically cleaned, rejetted, floats set and synced. When bike is warmed up it idles great and no stumbles through the power band. Unfortunately starting can be a pain. When I open the choke it seems it is entirely open or closed, there is no middle ground. It revs very high when open all the way but as soon as I start backing it down it just falls flat. The choke linkage is fine and the slides go up and down with no issue mechanically. When the bike is warm enough I can quickly close the choke but always have to run it @3-4K during warmup.
Any thoughts?

Spray some carb cleaner around your carb boots, after bike is at normal idle & see if it changes the rev's up or down, it could be a vacuum leak
wear goggles & don't smoke
Pete

My 83 KZ550 acts the same way. Full choke or none at all. Have to let it warm up for a full minute before I can push the choke off and once warm it has great throttle response. I've checked for vacuum leaks and have OEM filter and air box. I'm curious what you find out. I'm continuing to work on it though.

I don't know if it's relevant or not but I read a review of the 83 550, done in 1983, and the reviewer said the only complaint he had was that he couldn't find a choke position that let it run smooth when cold. But I've also heard of guys with similar bikes who had no problems or at least didn't mention if they did.

Yes, all or nothing, one of those quirks of the kz/GPz lineage. The CV carbs are nearly as bad for that too.

I never thrash them when cold so expecting it to be grumpy for the first mile on a cold start is no deal breaker for me.

The carbs on my 83 KZ550M are CV ... so yeah ..they are a PIA from my point of view.

Thanks to everyone for the info, ideas. I have sprayed for vacuum leaks without success. Will update if I figure out the issue or if it's something to just live with.