Trouble with VERY high idle

Well I have been in the process of getting my 82 KZ750 H (4 cylinder) up and running. I rebuilt the carbs and rejetted with a stage 3 dyna jet kit as I have a 4 into 1 pipe and pods. Was running fine, would idle perfectly at around 1000 rpm, but I started having issues with the idle racing after it got hot (shooting up to around 3000 or so in neutral). Checked the carb boots and yep, there was a vacuum leak around 2 of the boots. So I bought some new replacement ones, put them on expecting a good result and....

As I start it up now it immediately races to 8000 RPM. Engine sounds like it going to explode its revving so hard. So obviously that merited an immediate shutdown. tried it several more times, checking throttle wasn't stuck and each time it rockets right to 8000 rpm.

What in the world could I have done in just changing the carb boots to go from a solid 1000 rpm idle to forcing it to almost redline immediately?

Have you tried adjusting the idle at the carbs? Between carbs 2 & 3? Your idle screw could be too far in one direction.

First thought is something keeping the throttle butterflies from fully reaching the idle stop screw. Better double check the throttle cable.

Had my idle go haywire during a ride this evening. Happened while decelerating on an expressway exit ramp. When I stopped at the red light it was immediately apparent something got messed up. Idle would not drop below 2k on the tach, and it ran like crap...strange.
After limping back to the man cave, I was concerned the cam chain may have jumped a tooth, but my instincts suggested the carb sync may have been skewed, so that was where I began looking. Sure enough, one carb was out. So I made sure to exert a little extra torque on the lock-screw this time.
I am glad I listened to that idea rather than diving back under the cam cover, which would have been a complete disappointment to realize it would have been a thorough waste of time....and another gasket.
Amazing how a little bit out of sync can screw things up so much.

Got it sorted, thanks guys. You know the rule, check the simplest stuff first.... throttle cable was stuck. Didn't appear so at first, but it was. Actually seems like a good time to replace the cable anyways.