Slow return to throttle and hanging idle

Bike is an all stock 81 KZ650H. Started from not running to running on all four and starts up without hiccup. The last issues that I'm trying to diagnose are a hanging idle where the bike is fairly slow to return to idle and once it hits idle, will often not go below 1100. The idle adjustment knob is set all the way loose yet the engine still runs around 1100 or higher. Is that likely a need to bench sync the carbs?

There's a bit of slight backfiring when deaccelerating which I typically have associated with running lean. Only issues I know of currently is there is a small exhaust leak on cylinder 3 where the crush ring didn't seat correctly.

Also on a side note in case anyone has run into the issue before, normally on the carbs, you screw in a bolt that is supposed to hold the carb shaft in place (part 220) including a washer. However, on my carb set when I have the screw all the way tightened it pushes the carb shaft too hard and makes the throttle hard to push up/down. Anybody ever had issues with that? My backup carb set seems to not have this issue.

www.bikebandit.com/oem-parts/1981-kawasa.../o/m150572#sch426197

Hanging idle is typically an air leak. Some will say to spray stuff on the carbs and listen for a change in idle speed but that only shows gross leaks.

Regarding screw 220, you may want to try removing the top caps from the carbs and then loosen up the screws that bolt the slide to the shaft on each carb. Then tighten down that 220 screw and lastly go back and retighten up the slide screws.

Ah yeah good call on 220...didn't even think about going in reverse like that. I'll give it a try next time the tank is off. I had checked for air leaks before, but I"ll have to go over it once again to see. I know that the carb sync is likely off as well since the bike hasn't been ridden in a number of years, but at 150 psi on each cylinder, I somehow don't think it's anything major.

Just got thru chasing a hanging idle, as it turns out it was a bad throttle cable that really wasn't showing any visible kinks or wear spots and when pulled by hand open/close didn't seem to bind up. As a last resort I spent 13 dollars and the bike runs like it hasn't in a couple years. I'm guessing the cable has been going bad for a few years and I've spent hours going thru all the usual suspects. Maybe a long shot but could be worth a shot. It only took me a year and a half to give it a shot and sure wish I would have done it sooner

EZ

I have push/pull throttle cables that I am replacing in the coming days due to a high idle that hangs, especially after hard pulls to WOT 9+k RPM sometimes after several hard pulls the RPM will hang in the 3500k range for up to 10 seconds before settling down around 1500, that's with my pushing my throttle grip up as much as possible. I'll let you know if the cables help.