I'm having an odd problem getting my 1980 KZ440A LTD started first thing in the morning. It doesn't seem to matter what I do or where I set the choke, it will not start. Furthermore, I can only get it to pop out the exhaust if the choke is off/down, I hold the throttle open, and then let it snap shut. This causes the bike to pop a few times, and if I do this enough, eventually it'll start going enough to run on its own very poorly, where if I let it sit for a while it'll eventually be warm enough to run fine. If the bike is warm/warm-ish (cool enough that I can put my bare hand on the head without burning, but warm to the touch), it'll start up much easier without any fiddling with the choke/throttle. And any time I use the choke to start it warm, it fires right up immediately.
The start of this problem seems to coincide with replacing the carburetor boots/holders (the carb -> head ones) with new ones, as the old ones were leaky causing the bike to run very lean. This was confirmed with a can of carb cleaner sprayed on them, which caused the telltale idle rise. Prior to this replacement, the bike started up fine with the choke and would not start without it, although it would need to sit for a minute or so before I would be able to ride it and it did still exhibit typical lean-condition symptoms (high idle when warm, failure to return to the set idle point, popping from the exhaust on deceleration, etc). It was only after I replaced the boots that this problem got really bad.
My dad mentioned it might be the spark, but normally I've heard that coils work better cool and get less reliable when hot. I did replace the spark plugs (B7ES) a couple weeks ago (unrelated to this issue). And it seems odd that changing the choke would cause a difference in the behaviour too. I did try leaning the pilot jets all the way, put them at the standard 2.5 turns out, and the backed them out to the end of the adjustment range, all with no discernible change in the starting.
Another friend suggested it might possibly be the valve clearance. Does that seem likely?
EDIT: One other thing I just thought about is that it doesn't seem to matter if I set the petcock to PRI first for a few seconds or not. And when I come to the bike usually it's been sitting for less than a day (usually just overnight) and there shouldn't have been much evaporation in that amount of time anyway, right? Last time I could, I also pulled a plug after a few minutes of cranking and while there was a bit of gas on it, it certainly wasn't soaked or anything, so I don't think the mixture is off too much.
Thanks in advance!