REALLY high idle after carb disassembly

Hello everyone, been having some problems. Was idling at about 2k, but sprayed some starter fluid on the throttle shaft seals and found out one was leaking air. So I just got done breaking the bank apart and now when replaced it idles at 5K!!! holy cow!! This is with the one idle mixture screw (or throttle set screw whatever) all the way out. I did make one of the springs really tight that makes the throttle harder to pull, but that should make it stick shut better I would think. The sync is all screwy because I havent touched the screws (the three) since it was dissasembled, but can it not being synced cause this high of an idle!! Any ideas? Carb boots look fine, no cracks. Is this too high for even an air leak? any help is appreciated. Thanks.

 

if you broke the rack and didnt sync before you put the carbs back on, it can cause a high idle like that

 

High RPM's mean the Throttles are Open.

Check the Linkage for hanging-up on something.

Make sure the Throttle Cable attachment isnt wedged behind the Head.

Dont BEND or PRY anything ...

 

Yeah,you need to pull the carbs back off and bench sync.

 

If you took the throttle plates out when you replaced the throttle shaft seals you have to make sure they seat back in properly. The best way to check is to hold the carbs up to a light and see how the shines around the throttle plates. Its probably just one carb thats the issue.

MN

 

I got some suggestions from Chacal as well, through email. The springs are definitely installed on the right carbs, as after they were broken from the rack I only dissasembled their throttle shafts and springs one by one to make sure I mixed up nothing. Everything is on the proper carb.

My carb three spring is tight because It think I span the whole spring for more tention before tightening the nut that holds it on. It felt tight to begin with, but once assembled I realized its now tighter than it was.

I did open all the throttles (by hand pulling the throttle puller doodad) and made sure they were level when open once the rack was back together. Does anyone have a post on how to do a proper bench sync as I have no idea what this is.

With the spring that tight I doubt any of the throttles are stuck open, and when off the back they all opened and sprung closed fine, so I dont think any are stuck, but I've been wrong before.

Thanks for your help guys, I'll pull them again, but doubt I'll see anything differnt, thats why I'm posting.

 

You must properly balance carbs then colortune. If no carb balance or colortune kits, use a paperclip or slip of card or whatever to measure butterfly openings on the carbs while the carbs are still on the bench. Use the carb balance screws in correct order (see service manual) so that paperclips or whatever you're using has only a bit of friction when you're checking butterfly gap. This gives you a satisfactory carb balance, not perfect mind you, but very functional.
Next, turn out idle circuits 2.5 turns from fully closed. Once you've got the carbs on the bike, you can fine tune idle circuits for idle setting by turning them in or out.
good luck.
baz

 

But can them being out of synch, and mind you they looked pretty good on the bench. They all looked even to the eye, its not like one is REALLY open and the rest are shut, be causing 5k idling?!?

 

Yes, depending on the amount of diff in the openings.
The bench sync puts all as close to the exact same as a starting
point.
Then you fine tune from there.
Check the new seal... if it isn't seated prop then you may have a leak.

 

See Ricks bench sync.

He uses a businees card and cuts it up into 1/4" strips and you use them like a feeler gauge under the throttle plates whe you adjust the sync screws. Remember to start with #3 carb.

MN

 

Did you by chance put new needls and seats in your carbs? I know you did not mention that but that can cause the same problems you are describing if you are not getting the proper amount of fuel into the carbs. It will suck air in and cause the idle to run high. You will have to check float levels if that is the case. Just thought I would throw that one out there.

 

Are the slides free? If one sticks it could cause issues. There are several threads on carb cleaning and set-up on the site. They all refer to "clunk testing" the slides. Chacal has an excellent write up. When you get into carbs you can't do half the job and expect good results. Search the threads for a procedure and follow from start to finish. If you don't you will be here asking question after question. If you need to open a carb then you need to go through each and every step in cleaning, rebuilding, and set up.

 

Okay. After letting it sit for a few days (Because I havent had time to rip the carbs back off). It now idles at a decent speed. Could it have just been because of the carb cleaner and things in the carbs that made it run so high? Its still rough because I need to synch it, but I'm begining to think there is nothing MAJORLY wrong like I thought there was. And as for the clunk test, It passed before I broke the rack. They were all cleaned about 2 weeks ago. I just broke the rack to replace those seals, so It shouldnt be anything in the carbs, they were running fine as is. Its something to do with the rack being broken (and valves removed). Maybe I'll try to tune it now and see if its fine. Is it reasonable to think it was carb cleaner that would make it rev really high (makes sense if its exlosive).

edit: And no, the needles and seats are the old ones. The float needles seem to be set to the right level and dont leak.

 

Following a comprehensive Carb Cleaning, you should expect the Bike to "Perform" better.
Other factors will determine how well the Bike runs.
The Carbs need to be Tuned and Fine Tuned.
A carefully done Bench Sync will PreSet the Throttles for Idle.
Cleaned Fuel~Air Passages will insure the Idle can be adjusted.

If the RPM's are too high ... the Throttles are Open.
Try to get the Bike to Idle on the Pilot Air~Fuel Jets alone.
Once you get the Carbs on and performing without AIR Leaks, ... a Vacuum Sync will get you in tip top shape.

 

I am having issues with the high idle too.
-I just cleaned and re-built my carbs. I used strips of a notecard to bench sync the butterfly valves. they're all open almost exactly the same amount, giving just a little friction on the card.
-I went through Rick's whole nine yards carb tutorial and bottomed out the pilot screws before taking them out, and got very different turn amounts from each carb ranging from 1.5 turns to 4 turns. The bike ran alright over the summer, so it's possible they were correct, or else it's possible i miscounted. I accidentally started counting hand turns rather than actual 360 degree turns at first, so i COULD have miscounted, but not that drastically...
-I never had to take the carbs off the rack, so i didn't mess misplace any of the springs.
-i did a "clunk" test, and they all dropped just fine without catching on anything.
-the diaphragms on top are all good--no holes or anything.
-there were no holes in boots that I could see (but i'm not ruling out the possibility)
-I HAVEN'T put a manometer on yet to sync suction.

the story: I put the carbs back on yesterday, put some fresh gas in the tank, got new fuel line hose and a new filter. put the petcock on prime, cranked. no start. shot some starter in the intake. it started and stayed on. changed petcock to "on" (this whole time it's about 2k rpm idle). after 10 sec of being on rpms start climbing climbing climbing till 5k+. it's not warmed up after never running since October, so i get nervous and kill it. this happens a few times. i start it, it revs, i kill it.
I came back several hours later to satiate my curiosity. it cranks real easy, and idles around 1.5k. i'm thinking this is awesome and i'm gonna get to ride it soon. then it starts SLOWLY climbing climbing climbing until it's going up past 5k. i kill it. thinking it could be the throttle cable, i pull the cable out of the hanger (i KNOW that i didn't switch the choke and throttle cables, so lets rule out that possbility). so there's absolutely no throttle pulling those butterfly valves open. i crank it, same thing. just climbs.

my questions:
1) would this be caused by improper pilot screw adjustment. if yes, what are tips to fix them?
2) could this be caused by not having synced the carbs with a manometer? (i don't even know how i feasibly would with it screaming at 6k rpm)
3) what are other things that could be causing this that I've overlooked.

sorry for the long post, i wanna give you all the information i have. you guys have proven you know your stuff! please let me know what you think. I'm really excited to ride my seca again!

 

Hey jdoggsc. It can be one of 2 things I think in your situation. 1- Did you put new needles and seats in/ check float height before you re-installed carbs? 2- After I bench synced my carbs and put them on my bike it did the same thing you described. All you may have to do is adjust the idle speed by turning the idle screw I want to say it is counterclockwise. Either way when you start turning it you will know what way you need to go. Take it a little bit at a time to let the bike keep up with the adjustments. As the bike starts to warm up you will have to keep adjusting it. It may take 5 or more minutes for you to get it to idle fine. Hopefully that helped! Goood luck.

 

so if i just adjusted the main idle screw (the one attached to carb #3), would all the other butterfly valves follow? or would i have to adjust each of those individually?


what are new needles and seats? where in the carbs would those be? I did not check float height. I kept the same floats and kept the same fuel intake valves, so that all should be the same as it was before i started working on the carbs. I figured there isn't anything i need to adjust there. I just took it on good faith that the float levels would be teh same. It's POSSIBLE they aren't, but if it's the idle screw that's the problem, i'd prefer not to look at that until the semester ends in a month and a half (and i'd love to be able to ride my xj before that!)

 

The main idle screw that's between carbs number 2 and 3 will close all the blades. It's basically a throttle stop as the linkage rests on it when closed.

 

OK, update. I just turned the bike on and let it warm up. Just as before, it started and idled at around 1.5k rpm then slowly climbed. as it climbed, i turned said idle screw counterclockwise. The RPMs died down (~2K - 2.5k) and stayed there, but would climb again as it warmed up. I ended up incrementally turning the idle screw 20 times (little finger turns) which would have consistuted about 4-5 full rotations. I don't remember how much of an effect it had when it was doing the bench sync, but i'm sure the butterfly valves are all competely closed. by now.

I got it to eventually idle at 1.5k (normalish?) but every time i pulled on the throttle, it would jump up and stay there, and not come down. riddle me THAT! would incorrect float levels cause that?

 

I fought a similar issue on mine last year.

Float levels can cause it.

Air leaks can cause it.

Out of adjustment idle can cause it.

Out of synch carbs can cause it.

I had adjusted the carbs, synched etc and it would run great for as long as I left it sit still or short rides. Up and down the RPM's After a 30 mile interstate ride it would idle high about 2.5K I turned the idle screw out more and it worked. Took me a couple good long rides to get her dialed in.

 

LEAN, MEAN, and OBSCENE: THE CARB REBUILDING FAQ:


Question #1: Why Isn't It Running Right?:

Below is a semi-useful "general rules-of-thumb" list to help you recognize and diagnose fuel-mixture problems.

All of these descriptions assume that the carburetors are cleaned and opoerating properly, are stock (no jet kit), the valves are adjusted properly, and the engine has been synched.


Typical Symptoms of a Lean Fuel-Mixture Condition:

- Poor acceleration; the engine feels flat.

- The engine won't respond when the throttle is snapped open, but it picks up speed as the throttle is closed. (A too-large main jet also mimics this symptom.)

- Idle speed falls after you blip the throttle, then creeps back up.

- The engine runs hot, knocks, pings and overheats.

- A lean pilot circuit condition can be responsible for a creeping or hanging high idle, where the rpms stay high then slowly drop down to the set point.

- The engine surges or hunts when cruising at part-throttle.

- Popping or spitting through the carb occurs when the throttle is opened. Or popping and spitting occurs through the pipe on deceleration with a closed throttle.

- The engine runs better in warm weather, worse in cool.

- Performance gets worse when the air filter is removed.



Typical Symptoms of a Rich Fuel-Mixture Condition:

- Engine acceleration is flat and uneven and loses that "crisp" feel.

- The engine "eight-strokes" as it loads up and skips combustion cycles.

- The engine's idle is rough or lumpy, and the engine won't return to idle without "blipping" the throttle.

- An overly rich pilot mixture is usually the culprit when the idle drops low then slowly recovers.

- The throttle needs to be open continuously to maintain acceleration.

- Black, sooty plugs, a sooty exhaust pipe and black smoke from the tailpipe that stinks of unburned fuel.

- Poor fuel economy.

- The engine works better when cold. Performance falls off as it warms up or the ambient temperature rises.

- Engine performance improves when the air cleaner is removed.



Some common causes of a high idle:

- A vacuum leak somewhere in the intake system.....intake boots, internal o-ring seals, etc.

- Engine out of synch.

- Mixture screws not properly set or adjusted.

- Vacuum piston sticking or stuck in a partially raised position.

- Idle speed screw set too high, or set to create a "proper" idle speed when the engine was cold (and thus results in a "high idle" once the engine reaches operating temps). The idle speed when the engine is cold should be modulated via the use of the choke (enrichment) control system.

- Butterfly valves opened too far; synch screws out of adjustment.

- Throttle cable wear, adjustment, or throttle lever brackets installed incorrectly or interfering with other nearby objects (cylinder head fins, etc.).

- Choke (enrichment) circuit is stock "open"....this can occur even if the choke lever is rotated to the fully closed position, if for some reasons the choke plungers are not fully closing (cable wear, cable adjustment, or installation problems).



Question #2: What Parts Will I Need?:

The parts you'll need depends on what is there, what is missing, what is worn out, what gets broken or damaged during the dis-assembly process, etc., but the "basic items" needed for the rebuild process (besides any special tools and tuning equipment) is as follows:

- throttle shaft seals (you'll have to split the carbs from the rack to replace these).

- fuel supply tube o-rings (you'll have to split the carbs from the rack to replace these).

- float valve needle and seat rebuild kit (seat, needle, clip, seat washer).

- float bowl gaskets.

- idle mixture washers & o-rings for sure, and the idle mixture screws if damaged.

- jets, if damaged or incorrectly sized.

- carb bowl fuel drain screws, if damaged.

- new replacement carb hardware (screws, etc.)---now is the time to upgrade to stainless steel and/or allen-head fasteners if so desired!



From Our Experience:

Since the carburetors are THE most troublesome (and thus most expensive) aspect of these bikes, let me offer a few dozen words and insights about them, their service, and expense:

These carbs are quite simple, mechanically speaking.

The process of making DARNED SURE that you get them unbelievably, positively zestfully clean is a matter of stick-to-it-ness and resisting all attempts to take "shortcuts" or to brush off the tedious aspects of it. Many of the passages in these carbs are tiny, and it's that "tiny-ness" that bites most people, as they don't want to or don't realize the amount of effort that has to be undertaken to deal with such small passages.

If you read through these forums, you'll see many tales of woe of people who are now "cleaning" their carbs for the 2nd, 3rd, or 4th time BEFORE they get it right. The problem is, they never really "cleaned" them correctly the first, 2nd, and 3rd time. After all of the frustration and hassle involved, by the time they get around to the 4th go-around, then they understand that when people who have SUCCESSFULLY rebuilt carbs say things like "you'd better make SURE that you get clear flow through each and every passage, and you'd better polish that piston diaphram bore", etc. aren't just saying that to be over-the-top retentive about their own habits and style of working on these carbs, what they're really doing is issuing an experienced WARNING: do it right, or keep doing it again, and again, and again. And although they're kind of fun little critters to play with, taking them all apart and putting Humpty Carby all back together again, well, it's time better spent on other things.


Think we're kidding? The following thread is a "must read", because the title says it all:

http://xjbikes.com/Forums/viewtopic/t=17821.html


One last note: "cleaning" the carbs (internally, not just making them look pretty on the outside) is just one of the small subsets of tasks necessary to the proper REBUILDING of the carbs. I cannot stress this point enough. The use of the term "cleaning" is used as if it were the end goal of the process; in reality, the proper way to think about it would be this:

"A complete and exceptional level of carb CLEANING is a vital and necessary part of the process of properly REBUILDING the carbs."

And what are the other components of the rebuilding puzzle?

a) replacing the worn, missing, or necessary "wear parts" on the carb.

as noted previously...........



b) Proper "service" work to the carb bodies, especially:

- polishing the piston bore for silky smoothness.
- repair or clean up of any stripped threads in the carb bodies.
- replacement of any damaged or worn parts. In fact, the ability the recognize what is damaged and worn (besides the parts above which are designed to wear out) is the most difficult part of the entire task, since it requires a level of experience: are my needle tips worn? What, exactly, does a worn needle tip look like? How "smooth" is smooth enough? Etc. This is where the advice and experience of the members of this forum are invaluable.


c) Proper "settings" of the various components during re-assembly:

- the fuel levels (float heights).
- the "basic or bench synch" of the throttle valves


d) On-bike "settings":

- first and foremost, the measurement and setting to specifications of the valve train (shim) clearances. Failure to do this "wastes" 90% of your efforts involved with the carbs.
- final synch (using some type of manometer and the YICS tool if your engine is YICS-equipped)
- idle mixture screw setting, preferably using a Colortune plug.



One last thought about these carbs, since they are THE most troublesome aspects of these bikes, and something to consider:

- the four carbs concept is really neat looking, and is certainly performance-oriented to the extreme.

- for many of us who had lots of experience with automotive carbs, just beware that while these Hitachi and Mikuni carbs are a bit different in operation (and thus parts), a carb is a carb, and they're pretty basic little devices. The main difference is that the fuel circuit passages on these carbs can get bizarrely tiny, especially if you're used to working on automotive carbs (which have canyon-sized fuel passages compared to these carbs).

- like I've said, the cleanliness part is really just tedious work, with a couple of "tricks" thrown into the mix, given the small sizes you're having to deal with. The "rebuild" part is basic mechanical knowledge and skills, knowing which way to turn a screwdriver to loosen vs. tighten, when and how much force to use or not, being organized, stuff like that.

- but the "tuning" part will require some special tools, but no type of any rocket-science knowledge or skills----once you master the rebuild and tuning process with these bikes, you are pretty much a Carb Tuning God, as these carbs are about as "complicated" as it gets with carburetors. I mean, VERY few vehicles have multi-carbs, not until you get to the really high-performance machines level in the automotive world.

- well, as "complicated as it gets" until you start adding pods, etc.----which if you do, I sure hope you've got every last one of the basics listed above down to a science, and you can do it all, properly, and blindfolded, too!

- finally, if you do not have a service manual(s) for your particular bike(s), and you're going to wrench on it and want to do things right, then the only thing I can surmise from such a course of action is:

a) you're already an expert, or.....

b) you aren't really serious about doing things right, and that's okay, too---just don't expect good, quick, or cheap results!



The following guide may save untold hours of frustration and grief:

http://xjbikes.com/Forums/viewtopic/t=14692.html


*************************************************************

 

It doesn't need to be the Throttle Cable pulling on the linkage to cause the linkage to be opening the Throttles.
Misaligned Carb Bodies in the rack.
Clamps interfering with linkage travel.
Major Air leak(s).
Intake Manifold Leaks.
Leaking Manifold Seals to Cylinder Head (O-rings)

Something is Opening the Throttles to bring the rpm's to 5K.

Disconnect the Throttles Cable
Push DOWN on each of the 3 Sync screws after inspecting the Rack for any interference.

 

Might be one or more float valves not closing properly allowing extra fuel to creep by and causing the rpm increase.

 

wow that's kind of an overwhelming list of stuff it could possibly be. i was hoping it'd be something like "your air boots are leaking" or "you need to adjust your pilot screws" but it looks like we've successfully narrowed the problem down to EVERYTHING. It was 60 degrees late this morning and now it's snowing like a banshee so i had to cover my seca up again. I'll have pull the rack off again this weekend. thanks for the help. i'll keep you posted with what i find. hopefully that will rule out a few of the abovementioned possibilities.

 

so a friend suggested it might be just one cylinder that's whack and is pulling the rest along with it. He suggested I pull spark plugs one by one and see if i can find the culprit. I did. pulled spark plug 1 and the engine ran like normal. put it back on and pulled #2. the engine sounded weak. i skipped checking 3 for some reason, but #4 was the same effect as #2. i figured i'd found my culprit! cyl. #1! I put the spark plug back on all of them and cranked it go ensure that it'd do the same thing with #1 back in the mix with all 4 of the rest. it didn't rev anymore! it actually sounded and responded like normal! I'm happy that it's actually rideable now, but still a little unsettled because I don't know where the problem was exactly, or why it's fixed.

It still revs down slowly, but it DOES rev down, and quickly enough so that it's not a BIG issue when shifting. I'd still obviously like to get that fixed. Oh, it's running a little rich. what do i manipulate that and get it back to stoichiometric, or near stoichiometric?