Idling problems after rebuild

Hey Guys,

After rebuilding the carbs, and replacing a lot of the internal plastic/rubber bits -- the bike is idling very high. On start up, no choke, cold, it goes right to 5,000 RPMs.

Prior to the rebuild, last summer, it didn't have this problem, but it always ran on 1/2 choke and eventually only full choke.

I've wet-set the carbs within 3mm level of the carb body. I bench-synced the throttle bodies using strips of business cards. Since running it now, I've also backed the idle screw all the way out, and made sure neither the choke nor throttle cable is sticking. Still it idles high.

I suspect I have an air leak. I've found similar accounts to mine throughout the forums and web, but they're always slightly different. It seems no two xjs are alike in their temperament.

I've attached a 4-gauge sync tool to the carbs, all of the values on the faces of the gauges are different while the bike is running. Clearly needs to be synced, but I'm not sure if its worth color tuning it first to make sure they're all burning effectively.

To test for leaks, I've been spraying starter fluid around the front and back of each carb and have noticed when I spray around #3 (from the left) the RPMs tend to go up just slightly -- but nothing considerable. A leak is a leak though, I suppose. For a more reliable test, I'm going to use the propane method next. Rather than spray fluid wildly around the carbs.

I'm hesitant to sync the carbs in their current state, because of the chance of melting the rubber parts of the YICS blocking tool... I really dont want to clean a mess like that in the block.


Any thoughts on best steps to get the idle back under control?

 

Re: High idle after rebuild - best to colortune or sync first?

-Did you fully tear down the carbs, break the rack, and replace the throttle shaft seals?

-Did you submerge still partially-assembled carbs?

-Sync comes before any attempt to ColorTune.

-ARE YOUR VALVE CLEARANCES IN SPEC? If not then you're wasting everyone's time.

 

Re: High idle after rebuild - best to colortune or sync first?

Broke the rack, and realigned on a level plane.

I did not submerge the carbs in anything. I checked all small holes and crannies with my compressor's air gun, lots of carb cleaner, and a variety of different sized pipe cleaners.

For the sync, is it best to run for 30 seconds, and kill the engine following 1/4 turn adjustments to the carb throttle shaft screws?

The clearances have been checked, and the bike has had less than 50 miles on it since it was performed last season. I even had a witness, another forum member, Wirehairs, who can testify they were brought into spec.

I should add, lots of time was spent per carb body, ensuring all passages were clear, including the fuel bowl cover. I will add though, the only jets I hadn't pulled were the air compensator jets on the airbox side. They all seemed to be thoroughly entrenched - and I thought the size of their openings, combined with the passing of cleaning implements through them to the carb-hat area would seem to be a fine enough job -- they weren't the tiny passages I worked to clean in the covers.

 

Re: High idle after rebuild - best to colortune or sync first?

I should add, I did replace all of the throttle shaft seals, and they were greased before reassembly. Mixture screw o-rings were replaced. Diaphragms checked for holes (none!). Float needle, filter screw, and spacer replaced.

 

Re: High idle after rebuild - best to colortune or sync first?

SYNCH first, that will calm the engine down to where it can idle.

Then, colortune cylinder #1, then re-synch.

Colortune cylinder #2, then re-synch.

Colortune cylinder #3, then re-synch.

Colortune cylinder #4, then re-synch.

 

Re: High idle after rebuild - best to colortune or sync first?

if it's running that fast, drain the gas out of the float bowls so it won't start and get the sync close using the starter only. 15 seconds on the starter then let it cool a minute. keep a charger on the battery.
when you get it synced like that put the gas back on and your idle should be more reasonable and you can carry on with the normal running sync

 

Re: High idle after rebuild - best to colortune or sync first?

More like a butterfly holding open.

 

Re: High idle after rebuild - best to colortune or sync first?

After using a YICS tool, on removal of it I noticed that around cylinder 3/4 there was a significant amount fuel/oil residue. The same could not be said for the 1/2 cylinders. I didn't complete the sync because of the residue I found in the passageway.

I also discovered that the idle screw for carb #3 was considerably tight -- so I've decided to pull the rack once more and go over it. Also reexamine the rubber headers for problems to see if thats where my problems might be coming from.

I'll be sure to keep everyone posted on it...

 

Re: High idle after rebuild - best to colortune or sync first?

Crazy as this might sound, you may have to remove the carbs, loosen the butterfly screws just enough so you can "flip" the throttle mechanism and make sure the butterflies are seated correctly, then retighten the screws. I had the same problem after a full rebuild and this was the last thing I did to the carbs, after trying many different ideas, then re-benched sync'ed and all was well...did a vacuum sync and colortune after and the bike was great

hope this helps

 

Update - I pulled off the carbs, and the fuel bowls, additionally the idle mix screws, spring, oring and washer - because one of the screws was a bit tough to turn.

With the rack off the bike, I bench synced the rack, and can tell it was a much better job than my first go-round! Frustrating as all get-out, but much better.

I proceeded to check the jets in the bowls, and could see light going through them (still clean), and applied some anti-seize to the idle mix screws to aid in the ease of tuning.

I put them back on the bike, and now turned the idle screw in a few, and the bike was idling at 1100 RPMs!

The joy didn't last long... because whenever I tried to quickly twist the throttle, the bike died. If I went really easy on the twist, it would pick up and after 3000 RPMs, it would roar, even when you quickly blip the throttle.

Then it also started hanging on the idle, and periodically running up and down (hunting, I believe). You could hear it back firing periodically through all of this.

So, I'm led to believe the carbs need to be taken off, split, and gone through oncemore.

I'm curious to know what the consensus might be from the forums of my next steps.

Thoughts?

 

Did you perform a running (vacuum) synch after re-installing the carbs? If not, do that first.......it should be the very first thing you do after the bike starts and runs under its own power (the entire purpose of the "bench synch" is to simply allow the engine to start and run under its own power.....after that is accomplished, the bench synch has NO value and, in fact, the settings made during the bench synch process will need to be undone/modified in order to obtain a proper running synch).

An out-of-synch engine can/will exhibit all sorts of "problems" that will mimic issues of "other causes" on an engine that IS properly (vac) synched.

That's why you synch the engine first, as soon as it will run under its own power.

 

I agree but need to add:

Float levels? Did you accurately wet-set the float levels?

Then, as Len said, the next step after it runs well enough to warm it up is a running vacuum sync (with YICS blocked.)

Your symptoms are indeed those of an out-of-sync motor and/or wonky float levels.

 

I've wet set them to within 3mm of the carb body, per the steps laid out around the site.

Here are some shots of the gauges with the YICS blocking tool installed.

When the bike is off -- notice the #4 gauge a little different than the rest.



When the bike is running (high) on its own.

 

that's close but the righter you make it the better it will run.
don't be surprised if all your work goes down the toilet after your yics tool is removed

 

Polock, actually, it idles normally without the YICS tool. When I put it in, it goes up to 4500RPMs now -- when the photo was taken.

Also, I noticed some oil from around cylinder 4, on the YICS tool. I cannot imagine I'm supposed to be seeing oil come out of that YICS passageway...?

 

actually, it idles normally without the YICS tool
i'd say that means it's missing on one cyl with it out, with it in it fires, up go the rpm's. when it's cool and idling low, test for a colder exhaust pipe

clean the yics passage out real good. what your seeing might be old gas/carbon/who knows, that's been in there. you need a clean slate to figure out what and where it is/came from.
there's a o-ring on the yics port that should seal the port from the head to cylinders. oil would have to come from the head gasket, is there any oil on the back of the cylinders

 

I'm suspicious of the YICS tool being used. If it isn't properly sealing against the outside of the cylinder block it could be throwing everything off by causing a vacuum leak.

 

having the same issues with my bike, synching is a bitch i swear alot how ever i found that if i wiggle my wiring harness in the area of coil leads, by horn on right side of bike, same symptons, if i hold the wires a certain way its like a new bike shows up, runs normal constantly tuning searching fustrating almost gave up, towel, white flag, im tearing it apart tomorrow die eletric grease in hand, i believe this is a simple eletrical connections to coil leads or where it attachs to coil or something in this area, then good ol valve adjustment then sync, sync, sync, sync. oh and sync. kudoskun this worked for me i hope it helps... when you find it will be so simple you probaly kick the bike wouldnt blame you .

 

All,

It appears I had some bent ends on the idle mixture screw. Following their repair, the bike has been running solid. Idles well, runs up the tach like a champ of its day.

I knew the carbs were clean, and synced well. It turns out the tips are more easily/unexpectedly malleable than one might realize...

 

That makes total sense - the mixture was off and you couldn't regulate it.