Hanging idle

1982 SECA
Carburetors rebuilt to include throttle plate seals
Carburetors synced using MotionPro Sync tool
SECA “rod” in place during sync
Valves to spec
Compression 130-135psi across the cylinders
Throttle cable not binding
Choke or enrichment circuit behaving properly
No air leak detected

Problem: hanging idle and poor idle.
Attached is a video showing the return action of the diaphragm pistons
I am looking for feedback as to if the diaphragm assemblies are returning normally (they passed the clunk test prior to reassembly).
Also, any feedback as to other related issues that may be causing poor idle and hanging idle.

 

You didn't by chance have the throttle cable not seated on in the holder? That can happen sometimes when you put them carbs back in. The throttle cable end will hand on the top of the holder just a bit.

I hit my carbs with compressed air in the opening on top of the entrance to the carbs. This shows me is the diaphragms are sealed and working as they should.

Not too sure how many times you have cleaned these types of carbs? I will these carbs always humble me and my tech ability each and every new project XJ I get. They seem to have a mind of their own. Just keep at it and make sure to check and recheck all things. My first attempt at doing a XJ carb rack had me pulling it off six times.....yes six times and then it start to run like a dream.

 

Other than air leaks, sync, and a good rebuild hanging idle thoughts:

As Timbox suggested make sure you have cable slack in the throttle cable felt at the throttle grip

Does the idle drop if you push on the throttle linkage, which if it does suggests a hanging butterfly or shaft meaning more attention to the mechanical assembly

You didn't mention enrichment screws, so new O-rings there and set to the baseline 2 1/2 turns out from a soft seat?

Some bikes need the extra enrichment of setting the idle enrichment screws beyond the suggested 2 1/2 turns. I consider 4 turns the limit, but others may disagree with that. Either way, if you take them to 4 turns and it cures hanging idle you have good info if you want to pursue further

 

SIX TIMES! Damn, that means I have one more time to remove these things. The throttle cable appears to not be an issue inasmuch as I have the cable slack between the cable housing holder and the connection at the carb. Also, the idle adjustment screw is backed off. This is t my first rodeo, so I feel I have done a good job in cleaning the carburetors (I may be humbled at the end of the day).

 

Yes, applying pressure to the 1/2 adjustment screw seems to being the idle back in line but for the life of me I can’t seem to understand what I need to address. I removed the butterflies to change out the throttle plate seals; is there some trick to reinstalling them (I marked their orientation prior to removing them, so they were installed in the same orientation)?

Speaking of butterflies, I suppose in a perfect world, there would be zero clearances around each butterfly. I have very small areas around a couple of butterflies which I have not been able to adjust out. Is there something I should be doing to eliminate ANY gap between the butterfly and the carburetor or are the tolerances such that a butterfly valve may have a gap?

 

They need to be installed so they are centered and do not bind in any way, and this can get a bit tricky with a full rack because of the mechanical linkage used for syncing them. Normally, it is done with the individual carb during the rebuild process by leaving the two butterfly screws slight loose and fully moving the linkage to a mechanical stop and then securing the throttle plate screws. At this stage it is also very easy to tell if any binding occurs when fully closing the valve and opening it after the two screws are secured

With a full rack I think the process of doing one carb at a time can be done but you have to manipulate the linkage such that the carb you are working on leads the others in closing. You would then slightly loosen the butterfly valve on that carb and and use the springs action to pop it closed a few times before finally securing the two screws.

That may be overthinking it a bit and perhaps with a full rack if you set them up for a very accurate bench sync and then back off the idle screw so it is not touching, loosen each butterfly vale slightly, and pop the throttle closed a few times and then secure the screws again that would get you there

And just one other note I recall a few occasions where the nut on the throttle linkage on the #3 carb was tightened after the butterfly valve was secured and that created some binding and hanging idle

Here is a nice thread with solved hanging idle that has just about all the possibilities

https://www.xjbikes.com/forums/thre...s-clean-and-gasket-replace.84498/#post-503592

 

Thanks. More to ponder. At one point I felt the butterflies sticking but after fiddling (technical term) with the screws, they don’t seem to be sticking any longer. One remaining concern is the butterflies don’t seal; I can see daylight at certain points. Q: how much daylight is permissible?

 

Agree with Rooster 53 sounds like the Butterfly's or Throttle plates are hanging up or not set correctly.

 

Okay. Can I get some advice on setting the butterflies/throttle plates? This may not be the issue, but I want to address as many possibilities before reinstalling the carburetors.

 

Try it by doing a very accurate bench sync getting each throttle plate opening the same amount. There are varying methods to do the bench sync, I prefer using the transfer port in the carb throat

Then, back off of the idle adjustment screw so it no longer touches the linkage

Loosen the throttle plate screws just to the point that with a bit of force they could be maneuvered on the throttle plate shaft

Pull the throttle open and let it snap closed a few times

Secure the throttle plate screws - note blue loctite is preferred so once positioned properly taking one out at a time to apply loctite

 

Excellent response. Is it normal (or acceptable) that the butterfly doesn’t completely seal the throat of the carb? My butterflies cannot be adjusted so they completely seal off the area; the bottom half may fit perfectly but then a small portion of the top half will come to rest against the throat, thus leaving a very small gap on either side. Is this acceptable? This is the case with all four of the butterflies, so it isn’t a situation of just one or two butterflies are not fitting perfectly.

 

I have the four carburetors set as you suggested.

 

Should work and I suspect that you have a sync tool ?

 

The aforementioned procedure should center the butterflies the best they can be, but yes some light is still visible and I would consider normal