creeping idle after riding

I could have sworn I read another post on here with a member having the same problem as I, however, I can not find it for the life of me. So, here goes:

I took my carbs off my bike to clean them again, install new o-rings in each of the carbs idle fuel mixture screws, reinstalled all throttle shaft o-ring with silicone grease, bench synch the carbs, set the floats to within 1mm below the gasket (according to my factory XJ 700 N manual) and reinstalled on the bike.

I run through the entire vacuum synch procedure and get all 4 carbs pulling the same amount. Idle sits at 1050 - 1100. Colortune all of the cylinders so that I am getting blue flame on all.

I go to ride it the next day and it is WONDERFUL, that is, for the first 20 minutes or so. After this my idle slowly starts to creep from 1100 to 1500 (over a period of 10 - 15 minutes). The idle adjustment screw is all the way out (there is space between the tip of the screw and the plate on carb 3 that is supposed to push up against it to control idle). When I am riding and pull the clutch in, the revs drop to 3000 normally, but after that take several seconds to drop down to 1500. Also, when taking off from a stand still the bike bogs down until I can twist the throttle a good amount and get the revs above 2000.

I am stumped here. She rides PERFECTLY until I hit about 15 - 20 minutes in the saddle.

Also, I believe this is pertinent information, when I downshift (even before the problem arises) to use the engine to slow down the bike will decelerate a minimal amount and the downshift is extremely smooth leading me to believe that it may be running too rich.

All help is greatly appreciated (especially if anyone can point me in the direction of the post I am trying to find).

 

Sounds like you're getting extra air somewhere. When the bike warms up, and the idle starts creeping, try pushing down on the throttle shaft linkages and see if the idle drops. It's possible that you have a butterfly that's not closing all the way.

 

When doing the bench sync' you should make sure that the idle screw has enough adjustment to be able to back off & close the butterflys fully.
Check the 3 caps on the vac' ports, sometimes they can soften when warm & suck air, put double clips / cable ties on them.

 

Wizard you just said something I never read before and didn't realize on my own cause I'm AN IDIOT!
this point NEEDS to be added to Gamaru's sync thread
http://www.xjbikes.com/Forums/viewtopic/t=6366.html

I can't wait to redo my sync because I have a similar problem, NO CONSISTANCY. does the propane method for checking for an air/vacume leak really work? So you take a unlit propane torch and douse the surrounding area of the carbs with propane while running and if idle goes up you have a leak, true? Cause I never have a leak but the engine behavior constantly changes :evil: :evil: :evil:
the only good thing out of this is that my airbox boots are so soft, I can get all 4 on in less than 5 mins. But I'd rather have stiff boots and a steady running engine. I also can't get my plugs brown and I'm at 3.5 turns out. how long of a ride to change color of plugs, 5 mins good enough?

 

My 80 maxim 650 has this same problem. If I push down on throttle shaft linkage the idle drops. I have pulled my carbs several times to try to figure out why the butterflys seem to stick. The bike runs great though.

 

I had a very similar problem. I was pulling in air where it shouldn't be pulled in from. When I had renewed the o-rings on the fuel connectors between the carb bodies, I had "pinched" an o-ring and it wasn't seated properly. Difficult to see but what gave it away was the small drip of fuel I spotted.

Fixed that, re-synch'd and she was good to go. No more rev-creep when hot. Worth also checking the vacuum line from the petcock to the carb manifold too. Had a small crack a while back which gave similar problems.

 

Propane works for sure, but I find it's a bit hit & miss, I think carb cleaner with the fine tube can be more use, you can direct it better.
It only need a tiny amount of air to screw your idle.

 

Wizard - the caps on the vacuum ports have pinch clamps holding them on. The vacuum line from the petcock to the vacuum port is new and is also pinch clamped in place.

AndrewM - I am going to take the carbs off, check all of my o-rings and bench synch them one more time.

Rob-lit79 - When I was putting my carbs back together after installing new throttle shaft seals, one of my butterflies would sometimes stick. I found out that they have to be PERFECTLY aligned within the carb body before being screwed on to the throttle shaft. Check that out, it solved my sticking butterfly issue.

I will resynch the carbs with the idle adjustment screw in a ways and post my results.

 

Sounds like balky slides to me. Do all of yours pass the "clunk test?"

 

I'm having the same problem, but it's gotten worse in the last week. Rode to work, and at stoplights the rpms idled at 3000.

I'd already taken off the carbs, bench synched them with a lot of room for dropping the idle, and still had problems. Didn't clunk test, didn't really want to know the truth; I needed the bike to get to work, didn't have time to clean them.

I'm with bigfitz. It's gotta be dirty cylinders.

 

fitz - My carbs have been cleaned according to the excellent instructions by Rick. The bores (is this the correct word?) have been polished and the needle valves all pass the clunk test.

I took the carbs off, bench synched with plenty of room for adjustment in the idle adjustment screw. Set them on the bike to synch them and the revs shot up to 4k. I backed off of the adjustment screw and had it going nice and good at 1100 RPM. The entire synch process took me roughly an hour. The bike was running for a majority of this time and kept the idle steady. As soon as I had everything set and colortuned, I took it for a ride and about 10 mins later the idle crept up to 1500. The idle adjustment screw is all the way out at this point.

I tried what what rob-lit mentioned and pushed down on the throttle linkage between carb 3 and 4 (easiest to reach) and if I held it down, it would keep idle at 1000. As soon as I let go it would shoot up to 1300 RPM and then move back up to 1500 RPM.

I am going to check my throttle cable for binding. What else should be checked?

Also, before I bench synch and screw the synch screws all the way down and try to open the throttle it will stick in the open position. As soon as I back off all 3 screws a bit, it will snap back closed. Is this normal?

 

Did you split the rack? if you did they can go back slightly different & cause the butterflys to stick. (It says so in the manual)

 

mestnii, I shouldn't talk cause my bike still isn't perfect or the way it should be But, during my last bench sync I found that the #1 butterfly was touching on the top of the venture where the others were sealing on the bottom. I loosened the two butterfly screws and tried to slide it down a smidge cause the holes are kinda elongated, ended up having to turn the butterfly around (even though Rick says not to) and it matched the others much better. Because you can never trust that the last guy put it back together correct.
So to get them all the same, I did the bench sync with the spray tube froma WD40 can and then held them up to the light and moved the throttle lever. if the idle screw is backed out all way you'll be able to see if all the light shuts off/goes away at the bottom of each butterfly simoultaneously. when it didn't I made fine adjustments on the sync scres, 1/4 of a turn and such until they were all identical, all the light goes away and comes back under the butterflies at the same time when throttle is actuated.
if you look, let me know if you found this difference

 

Hmmm. Our destinies intertwine. Cleaned my carbs pretty thoroughly, all cylinder bores pass the clunk test. Still idling too high.

What are the most common sources of air leaks?

How do you tell between airleaks and stuck butterflies?

 

And, does anyone see a problem with using the bike while this is going on? I could see a greater chance of over heating in traffic, but I can't think of anything else that could happen from a high idle.

(It's my only motor vehicle.)

 

depends on how high the idle is and if it comes down realitevly quick. so how high and how long? The leak could come from the intake boots that bolt to the cylinder, or any rubber part on the carb that air could get by. Also the boots that go to the airbox and it blows my mind but this is my first 4 stroke so I'm learning. I could see how the air on the rear of the carbs could change the mixture by making it lean but I've heard it could mess up the idle, I guess they're related but my bike acts crazy! and I'm probably going to replace the intake boots next. I used the 1 1/2 rubber couplings for the rear boots and they work AWESOME. it's a recent thread you can find if you want

 

well, if you downshift with that high idle, you could accidentally panic when you have to use more brake to stop and hit a cage.

 

I broke the rack apart to check that everything was square and level. I think that carb 2 was off center and hence did not allow for an even adjustment of the idle/caused it to creep when warm. I adjusted it so that I have more than 4 full turns of idle adjustment either way and all butterflies seal completely when the idle adjustment is backed all the way out. Checked all of the o-rings as suggested. All were fine.

Oak- I recommend taking your carbs off the bike and checking them with a level. Get one large enough (I used a carpentry level) so that you can lay it across all 4 carbs and make sure that the hats and outlets ALL TOUCH the level. I made a mistake at first and only had carb 1, 3 and 4 touching the level but it still showed me that the entire rack was plumb.

I will re-install tomorrow and deliver my findings.

 

I don't see how the rack could be out of level when there are two brackets to hold it in only one position. I know it's possible but I couldn't take mine out of level if I tried (once the screws are tight)

 

Anything is possible when I get my hands on it

Just synched and colortuned... going for a ride.