Slow throttle return

As suggested vacuum leaks are common for this. But also carb sync, or lean condition can cause this. Fuel levels and running vacuum sync should be checked.
Can you push back on the throttle linkage at the carbs and have it slow down?

Ok; it sounds like you've tested for a lot of the usual causes already. Here's one other question - assuming you still have the push/pull throttle cables, when the idle hangs up if you twist the throttle to the "closed" position does the engine idle down immediately? Ed

Carbs are cleaned, synched and adjusted though.
Yes, I can slow it down by pushing the pulley manually. I can also feel that there is a resistance when I try to pull the pulley by hand.

Motor Head wrote: As suggested vacuum leaks are common for this. But also carb sync, or lean condition can cause this. Fuel levels and running vacuum sync should be checked.
Can you push back on the throttle linkage at the carbs and have it slow down?

Yes, I have. I can force the idle to come back by twisting the throttle back but not significantly. It's weird because I could at least twist back the throttle and rev back the rpm by throttle a couple days ago, but now it seems that it's not effective anymore.

650ed wrote: Ok; it sounds like you've tested for a lot of the usual causes already. Here's one other question - assuming you still have the push/pull throttle cables, when the idle hangs up if you twist the throttle to the "closed" position does the engine idle down immediately? Ed

Since it will slow/ return with a bit of pressure on the linkage. Have you checked to see if there is still adjustment for the Idle Speed Screw? Can you still back it out and have the Idle drop? If not the Slides may well be adjusted to High on the Crossbar Linkage. This will keep them up, and not allow them to return fully.
Otherwise sounds Lean, this will make it Hang at High Idle.
Did you recently change the Air Filter housing/ Box to "Pod's"?

As Kidkawie suggested you may want to clean and lube the ignition advancer (if you haven't already done so). When they get sticky they can cause odd symptoms. Ed

I'm not familiar with your carbs, but if you can: remove the carb caps and spray some WD40 around the slides, work the throttle while you're doing this to saturate the slides. Start it up and see if it changes. Otherwise, it's a vacuum leak or dirty advancer. You need to totally disassembele the advancer, clean and lube with some lightweight grease. You can't tell if it's dirty just by moving the weights with a screwdriver.

I can drop idle by twisting the adjuster.
The bike came with pods when I bought it, but the jetting was stock. It wasn't running right, so I re-jetted myself. 120 main, 22.5 slow, 1 1/4 turn out for mixture-screw, and needle clip in the middle.
The bike idles smooth and pulls hard at all speed except 1/8-1/4 throttle gives me out-of-gas symptom. I was going to play with the needle to see if I can get rid of the symptom, but slow return problem got in the way.
I think I ought to check everything from scratch.

Motor Head wrote: Since it will slow/ return with a bit of pressure on the linkage. Have you checked to see if there is still adjustment for the Idle Speed Screw? Can you still back it out and have the Idle drop? If not the Slides may well be adjusted to High on the Crossbar Linkage. This will keep them up, and not allow them to return fully.
Otherwise sounds Lean, this will make it Hang at High Idle.
Did you recently change the Air Filter housing/ Box to "Pod's"?

Ok, I will check one more time and see what happens.

650ed wrote: As Kidkawie suggested you may want to clean and lube the ignition advancer (if you haven't already done so). When they get sticky they can cause odd symptoms. Ed

When I was rebuilding and setting the timing, I did not lube the parts as I assumed that all the parts look and feel good. I am going to get in there one more time and check everything. I will try the WD-40 around the slides, too.

Looks like I'm gonna have busy weekend. Fun

Kidkawie wrote: I'm not familiar with your carbs, but if you can: remove the carb caps and spray some WD40 around the slides, work the throttle while you're doing this to saturate the slides. Start it up and see if it changes. Otherwise, it's a vacuum leak or dirty advancer. You need to totally disassembele the advancer, clean and lube with some lightweight grease. You can't tell if it's dirty just by moving the weights with a screwdriver.

If not done yet, disconnect the cables, start the bike and manipulate the carbs by hand, see what happens.

Richie7 wrote: 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.

Stock pilot jet is 17.5

Good Fortune!