KZ750 1982 Idles super high when warming up

Hey guys, first post on the site since I didn't find any solution elsewhere... hope you can help me!

I have a KZ750 1982 with new air filters and new vaccum rubbers. I start it using the choke and release it gradually. When the bike gets warm (after 5-10min without riding it), it starts to idle super high by itself going from 1300 to 4000 + until i turn it off. The idle gauge is unscrewed to the max and the throttle cable seems to be working fine.

Any ideas?

Thanks.

aftermarket air filters?

nop, brand new.

what happens when you mess with the idle thumb screw after the bikes warmed up. If you turn it does it affect the idle?

Right now it's unscrewed to the max. If i screw it in, the idle keeps going up...

Right now it's unscrewed to the max. If i screw it in, the idle keeps going up...

sounds annoying lol. If it were me I would just go through the list.
-If you've altered anything on the bike lately check that area and areas it directly affects. Make sure its all how its supposed to be

-Always make sure your carbs are clean and free of debris

-make sure all vacuum lines are all hooked up where they need to go or are plugged.

-throttle linkage. Make sure the bracket on the carbs that the throttle cable connects to is hooked up right. Mine has just a tiny bit of play in the cable before it actually opens the throttle plates.

- check for vacuum leaks with whatever spray your comfortable with (carb cleaner, wd40, starting fluid) when checking, make sure your bike is warmed up fully and make sure and check everywhere. the rubbers between the carbs and head, rubbers between air box and carbs, spray all up and down the vacuum lines

to me it sounds like an erratic vacuum leak. I had one on some whooped rubbers between the head and carbs. it didn't get as wild as yours but it was very difficult to find as it would only appear when the bike was warm and i kind of jiggled the carbs while spraying Check everywhere. Hope this helps or at least gets you started

Any mods on the bike? When did the problem start/how longs been going on?

Yeah i will go thru that list. Such a weird problem... Thanks!

No problem. Hopefully you get it sorted out. It really sounds like nothing major though. Let us know how it goes

If the idle is climbing when the engine is warmed up and the choke is turned off that means you have a lean condition and most likely a vacuum leak.