Slow throttle return

Motorcycle:
1976 Kawasaki KZ900 A4

Carbs:
Mikuni 26mm with K&N oval filters(Main-120, Pilot-22.5, Needle clip-in the middle) Cleaned, rebuilt with new parts and lubed.

Problem:
Slow throttle return WHEN THE ENGINE IS RUNNING. Snaps right back when the engine is not running.


I can visually confirm that the throttle pulley slowly returns when it just hits the idle adjuster. The symptom is more obvious when I blip the throttle just a hair touch. All the linkages have been cleaned and lubed. I replaced the return spring. I checked all the places that relate to the linkage system, but no luck. The only thing I can think of is the throttle valves being worn out causing escaped air between the valves and carb bodies. Is this possible? I appreciate all your advises.

UPDATE: I took off push&pull cables to see how the linkage works without. Pulley moves freely without engine running. When the engine is running, I can definitely feel resistance at the lowest point with my finger. After passing that point, the pulley moves freely. Same thing coming back to the lowest point. I have to push the pulley to completely seat the slides.

Remove the "push" cable, see if it helps.

If it does, adjust the pull cable for normal operation. Then gradually adjust the push cable, once the action becomes slow, back off the push cable adjuster and lock it down.

It could also be a sticky ignition advancer if the carbs check out ok. Lots of posts about the advancer on this forum. Cleaned mine to fix a hanging idle.

Another thing to check is vacuum leaks at the carb holders. Test for leaks is described on this forum, but ask if you need instructions. Also, if you want to totally eliminate the possibility of hanging cables you can unhook them both at the carbs and see if the problem persists. If it does you can scratch cables off the possibilities list. Ed

I really thought that it was the throttle cables, too. But it wasn't. I checked the timing spring, too. The linkage works smooth when I'm not running the engine. It's really strange..

I put brand new manifold boots and tested about a week ago. No secondary air. Thank you for mentioning it though.

650ed wrote: Another thing to check is vacuum leaks at the carb holders. Test for leaks is described on this forum, but ask if you need instructions. Also, if you want to totally eliminate the possibility of hanging cables you can unhook them both at the carbs and see if the problem persists. If it does you can scratch cables off the possibilities list. Ed

Do what Ed says and run it without the cables.

Vacuum will pull the slide towards the motor.
if their worn and ruff on the intake side they will
drag and can act like your's.

Yap, I've done it but no go.

Kidkawie wrote: Do what Ed says and run it without the cables.

Should I just go ahead and replace the slides or does that mean that the carb bodies might also be worn out?

zukdave wrote: Vacuum will pull the slide towards the motor.
if their worn and ruff on the intake side they will
drag and can act like your's.

Richie7 wrote: Should I just go ahead and replace the slides or does that mean that the carb bodies might also be worn out?

zukdave wrote: Vacuum will pull the slide towards the motor.
if their worn and ruff on the intake side they will
drag and can act like your's.

Could also be varnish on the slides/carb bodies. It would be worth pulling the slides to clean and have a look. Just my .02 here so take it for what it's worth. If I needed new slides in a set of 26s I would be looking for a whole new set of carbs. IMO the 26s aren't worth the expense of new slides. Plus if the slides are that beat then the carb bodies can't be in very good shape themselves.

Edit: I see where you said the carbs were cleaned. Did you inspect the slides at the time?

Yeah, I noticed that I would be paying more for new slides than a used carb set. I did inspect the slides, and I thought they were just about right. Not much play, but not too tight. I could definitely be wrong as I just used common sense to determine that decision. I'm still learning my KZ I have already posted in the "Wanting" section . Hopefully, I'll find a good set here.

testarossa wrote:

Richie7 wrote: Should I just go ahead and replace the slides or does that mean that the carb bodies might also be worn out?

zukdave wrote: Vacuum will pull the slide towards the motor.
if their worn and ruff on the intake side they will
drag and can act like your's.

Could also be varnish on the slides/carb bodies. It would be worth pulling the slides to clean and have a look. Just my .02 here so take it for what it's worth. If I needed new slides in a set of 26s I would be looking for a whole new set of carbs. IMO the 26s aren't worth the expense of new slides. Plus if the slides are that beat then the carb bodies can't be in very good shape themselves.

Edit: I see where you said the carbs were cleaned. Did you inspect the slides at the time?