Slow return to idle

Hello everyone,
Putting my xj650G back together and I'm almost there, just did rebuild on my carbs got them back in, and now tuning. So far so good, my first running sync is spot on and the pilot mixture are close.

But I have a concern that it does not fall back to proper idle when I go off throttle. I've had the rack out once to make sure that the throttle plates were not binding etc i made very sure they all closed completely. I did that by looking down the throats from the airbox side to gauge by the light passing the edges, which was very little, also equal across all carbs, so I assume no binding.

When returned to a higher idle, I can press on the linkage near where the idle screw contacts, and get the idle to drop back down. I can also do it by using pliers on the throttle shaft by the c clip and rotating the shaft forward.

looking at the throttle cable, there is slack there so I'm sure that's not that cause.

It seems there is not enough spring tension to close the throttle plates it completely, although I would not have thought so with the carbs off the rack, they snapped back very well with complete closure.

When I assembled the rack I just put the springs on and rotated the shafts about 45 degrees to put the screw holes in the right position. I assumed that was the correct spring tension.

Sorry for saving this for last, I have tried backing out the idle screw so thats not it either.

Any ideas on what I can try to correct this?

Thanks in advance

Bob

 

Okay, so in my experience tuning carbs in general, there are a few things that causes this. I would start with idle speed screw, I did read your post and saw you said that you adjusted it. Vacuum leak is another possibility. Check all your vacuum caps, lines, boots, ECT. While idling spray water over the boots and such see if your bike dies. Preferably in localized areas so you can pinpoint. Also throttle cables could be lubed. Lastly, and this one will sound dumb, the throttle grip itself could be binding on the handle/housing. Best of luck.

 

Thanks for the response. I lubed the throttle cable and I believe its better but not 100% as I can still press on the throttle linkage to drop the rpm.
Got an idea from a YouTube video where the gentleman rotates the throtle shaft a turn to load the spring before attaching the throttle plates. I believe this is the step I missed that may be the root cause of my issue, I wi pull the rack and redo and report back.

See 5:26 into this youtube video



Bob

 

It's alos possible that one of the throttle plates is rubbing on the carb body. Check that before you go tearing the rack apart again.
To get them to seat properly you'll back the screws off enough for the plates to sit slightly loosely, then work the trhottle linkage a few times so they settle into place.

 

Thanks for the tip.
I didn't quite do it that way the first time I will follow those instructions when I take the rack off
Btw,
I got some items back from paint today. Here's what we are working with.
Bob