#2 and #4 not firing after rejet

[hp1000s]

This might be dumb, but, could the replacement bodies be the ones that have open vacuum ports for the fuel petcock?

 

[J_C]

Carb #2 (Replacement) has the vacuum port to the petcock... why, what are you thinking?

 

[hp1000s]

Like I said, dumb, but if you've got open(to atmosphere) vacuum ports, it could lean mixture as well as disturb the vacuum signal for fuel delivery through idle circuit. It was just a thought, 'cause I'm no expert on CV carbs.

 

[KEITH KRAUSE]

Like I said, dumb, but if you've got open(to atmosphere) vacuum ports, it could lean mixture as well as disturb the vacuum signal for fuel delivery through idle circuit. It was just a thought, 'cause I'm no expert on CV carbs.

I think you're talking about float bowl venting. No vacuum present, just venting. The common practice when running pods is to remove any float bowl vent lines and leave the vent ports open. If you don't remove them, a vortex effect forms in the lines and can cause the fuel level in the bowls to lower/fluctuate and the result is fuel starvation. This condition worsens in crosswinds and while freeway riding. Some carbs suffer from this effect more than others. The VM carbs are very sensitive to it, the CV's seem to be less effected but still effected.

 

[KEITH KRAUSE]

Thanks folks, I'll double check the coil and the bypass ports,

Not sure how the bypass ports would be clogged as I soaked them in carb cleaner for severals hours each, but I'll see if I can indetify them and blow some air through there

The bypass holes are very small and sometimes don't clean out well without special attention given.
They are right where the upper throttle plate nearly touches the carb throat.
The reason I mention these is because it would be easy to check for one thing.
My reasoning is because you say you tried to idle the bike, then noticed the two cold cylinders. Obviously, you're on the pilot circuit COMPLETELY at idle. If no gas is wetting the plates/cylinder/plugs, then the pilot circuit must be plugged somewhere or there's a vacuum loss. You said the carbs were taken apart and all jets replaced, all carbs recieved the same jets/parts, I assume very clean. That SHOULD rule out any dirty parts/jets and that just leaves the possibility of the replacement carb bodies having dirty ports.
If the entire pilot circuit is clean, then the only reason fuel wouldn't reach through the clean pilot jet/passages to the carb throat, is a vacuum issue not drawing fuel.
I believe you also said float levels were set to factory levels.
I've never liked swapping carbs from different years/models. There can be small differences that many of us just aren't aware of, but can cause problems. Not lecturing you, I know you're just wanted to replace the bodies because of the stripped mixture screws. But I've read many times before that unknown problems come up with carb swapping.
Hopefully, we'll figure the problem out.

 

[J_C]

Hey guys... took the plugs out after cranking for about 10 seconds.... they didn't really smell like gas.. more like oil? But then I took one out for comparison, and it didn't smell like gas either.

Decided I'd try to start the bike up.... 1, 2 and 3 heated right up!! I'm not sure if that's because the idle is set high right now (it was running about 3000 rpms) so it may have been skipping the idle circuit?

The interesting news is that #2 was from yogib... and the #4 was from the 82 gs1100... so maybe it is just passages instead of bodies. I'll take the plugs back out once it cools a bit, try dropping the idle and see what happens as well. Then I'll pull the carbs to see if I can do anything else about those passages

 

[J_C]

#2 fired again on low idle so I think that one's in the clear! We noted that the 1,2 and 3 carbs had fuel on the butterflies and there was fuel on the inside of the hoses going to the block. #4 was dry on both areas as well as the plug. Obviously fuel wasn't getting through.

I finished using a wire to clear out the pilot circuit holes in the venturi. I also blew a bunch of air through there via the pilot jet hole, and replaced the pilot jet with a cleaner one. Tomorrow I'll start it up!

 

[KEITH KRAUSE]

Sounds like you're making progess. Gotta have fuel in the cylinders to get combustion. I'm assuming you have good spark at this time to all four.
Now just find out why the 4 carb isn't delivering fuel and you should be ready to synch and test.
If you've got spark, fuel and a good bench synch and the idle adjusted enough to start, it should start up and you can vacuum synch.
Be very careful with cleaning wire. The carb material is fairly soft. Squirt lots of cleaner and lots of air to get those ports/passages clean. I use 150+ psi sometimes.

 

[J_C]

Hrmm... Well it started right up this morning, but still no #4. I swapped the #1 and 4 plugs just to double check, 1 still worked, 4 did not. Did a compression test on a warm block. 150psi, so that also seems pretty acceptable. Back to the carbs again

I'm going to go down and buy some carb spray, though I don't have compressed air. Looks like I'm rebuilding the carb again.

I'm also dipping the old broken #4 in the hopes that it might be able to be jbwelded and used for comparison.


EDIT: oh I also checked the boot and butterfly and it seems that fuel is getting to the cylinder now... just must not be enough?

 

[J_C]

Hrmmm Developments!

I completely broke down #4 and went to town with the carb spray. I hit almost every passage there is multiple times and manually blew them out. I had a really good feeling when I reinstalled the carbs and......

No It didn't heat up. In somewhat mild frusteration I cranked the throttle to see what the other carbs were made of and... low and behold... a continuous backfire in the right pipe! My father (partner in crime) reports that the #4 header has suddenly become very hot. #4 is (back)firing! I drop the revs from 6000 back down to 2000 and the backfire lessens but is still hanging in there. I drop back down to idle and it goes away. It may have completely stopped firing all together, but I won't know until I let it cool and go fire it up again.


Backfiring.... this is certainly new.... \\/

 

[KEITH KRAUSE]

Just saw your update. Quick reply 'cause I gotta go out.
Trying to make sense of your latest test...opening up the throttle as you did would certainly bypass the pilot circuit (and any fuel flow problems the pilot circuit may have). You'd be running on the jet needle at that point. Your test suggest you got more fuel into the cylinder. So that's good.
The backfiring isn't good though. Most backfiring can be from raw fuel collecting in the cylinder and exhaust and at some point the whole collection combusts in one big bang or smaller bangs. Problem is, you say there was no fuel entering until you decided to open up the throttle. No fuel could have collected before you opened it up. If that was true, then your needle circuit also has a problem and/or, the spark is intermittent. I say this because your test was while running on the needle circuit.
A weak spark will obviously cause backfiring but so will too much fuel.
I don't have time now but I'll try to think of the problem and come back later if you still need help.
Something's causing poor combustion and it's not compression. So that leaves a weak spark or carb problem. 1 and 4 are fed by one coil, so it suggests the coil isn't the problem (1 is supposedly good), but it's still possible that other conditions/differences exist between cylinders/carbs 1 and 4 that help #1 keep firing, though it may have a weak spark too.
Do you have a manual and multi-meter? Test the coil resistance's and voltage first because it's simple. If it passes test, then you just have to check/clean any plug cap or plug lead problem. That would cover any #4 spark problems. HOWEVER, I'm not that familiar with the ignitor tests on your bike. Seems to me the ignitor can cause a weak spark at two cylinders also. Anyone? Perhaps your manual will help?
Anyway, check the coil, plug connections and possibly the ignitor. Basic maintanance that should be done anyway. If it passes, you KNOW it's carb related and we can focus on that. If you have a meter, the electrical tests are much quicker/easier than tackling the carb.
Hope I'm not making you do any unnecessary work, but backfiring can be either fuel or electrical and we have to eliminate one so we can focus on the other.

 

[J_C]

Keith, thank you for your replies!

I do have a multimeter, though I'm unsure why the problem wouldn't have followed the coil / cap to #1? That's why I haven't focussed on that earlier than now, though I can certainly look into it.

Before doing that, however, we just noticed something else when we went to start it cold...

We put it on choke for around 30 seconds, #4 did not heat up. I closed the choke and opened the throttle just partially (my idle adjust knob threads are warped so they dont work right). As soon as I closed the choke and went to normal idle, the backfiring (is it backfiring? Its a loud popping coming out of the pipe) started and the #4 heated right up. Is it possible that the choke for whatever reason isn't working on the #4 and it isn't until it's on normal idle that the combustion begins happening, resulting in the burning off of all the fuel already there?

The popping was happening at 1500 rpms, which I assume is still only the pilot circuit, since I only had the throttle cracked enough to keep the bike running. Does this pose any additional clues that a guru such as yourself might be able to use?

 

[KEITH KRAUSE]

Keith, thank you for your replies!

I do have a multimeter, though I'm unsure why the problem wouldn't have followed the coil / cap to #1? That's why I haven't focussed on that earlier than now, though I can certainly look into it.

Before doing that, however, we just noticed something else when we went to start it cold...

We put it on choke for around 30 seconds, #4 did not heat up. I closed the choke and opened the throttle just partially. As soon as I closed the choke and went to normal idle, the backfiring started and the #4 heated right up. Is it possible that the choke for whatever reason isn't working on the #4 and it isn't until it's on normal idle that the combustion begins happening, resulting in the burning off of all the fuel already there?

The popping was happening at 1500 rpms, which I assume is still only the pilot circuit, since I only had the throttle cracked enough to keep the bike running.

OK. As for the first part of your reply, yes, a weak coil will effect both cylinders it feeds, but, I've seen weak coils have a more noticable effect on one cylinder more than the other because of other conditions that effect spark. You CAN have one cylinder with apparently no spark and the other cylinder can have a weak spark but still firing. "Other" conditions can be lots of things I won't get into now. If, at the exact time the problem is happening, you should at least remove the suspect plugs (1 and 4) and look for a blue spark. That may tell you enough. But it's still best to also test with your meter and follow your models manual info. This is just basic checking/troubleshooting. With what history I know of this bike, I tend to think your problem is carb related, but it would be nice to know the electrical is good and we can focus on just that replacement carb.
If you read any of my posts, I'm a real believer in going through the basics when there's a problem. It may seem like more work, but I always look at it as it needs to be done anyway and actually saves time sometimes instead of looking for things one at a time. Basics are compression, good valve clearances, good spark/resistances/voltages/timing/connections, VERY CLEAN carbs with good inner o-rings/rubber parts, floats set, bench synch followed by vacuum synch, good manifolds/any manifold o-rings, clean air filter, and any other things that your bike's mod's may require.
Anyway, back to your latest cold start up results.
Yes, it's possible your choke isn't working, but I don't think that's your main problem. I tend to think your #4 choke is working. You can see the mechanical movement/operation? When they "fail", it's usually because they won't seal and you run rich. If mechanical, it's usually obvious just watching it and comparing movement to the others. Many things effect cold start up so it's not easy to make sense without being able to see the bike myself. Temperature, engine temp, mixture screw adjustment, amount of choke, clean carbs, etc, all can change things.
If the throttle is closed, you're COMPLETELY on the pilot circuit with ASSIST from the choke circuit. The moment you open the throttle, this effects vacuum/pressure and the choke circuit is bypassed. SOME choke circuit fuel still enters but you're still bypassing it to some extent and the more you open the throttle, the more the choke is bypassed 'til it really supplies an insignificant amount, if any.
AS for opening the throttle "a little", most jetting charts will say that you're mostly on the pilot circuit but the jet needle will start to overlap very soon. So it's not a positive thing to say "I'm at 1/8 throttle... so I must still be 100% on the pilot circuit". I've seen varying results as to how early the jet needle starts overlapping the pilot circuit.
In your test, backfiring is better than no firing. If it won't fire at all until the throttle is opened somewhat, this suggests that the increased vacuum is drawing fuel from the jet needle at least partially. It also suggests the pilot circuit isn't operating right and there's not enough fuel in the mix until you open the throttle, which will (depending on how much throttle) at least start the transition from pilot to needle circuit. The bike SHOULD get all the fuel it needs at idle if the pilot is operating right. The choke will be needed for starting, but it always depends on how cold it is outside, etc, as to when you can shut off the choke and hold an idle 'til it warms up well. My bike only needs about 30 seconds of choke this time of year.
Remember, I'm assuming the floats, o-rings, synch, etc, are all good. I assumed earlier that the carbs were clean, but it appears they may not have been. Also, you can't be sure any small passages are clean without compressed air. You can try to verify by watching for carb spray exit a hole whenever you shoot it into a passage but that still doesn't mean the passage is completely clear. If you don't have access to compressesd air, the best you can do is spray or soak, then carefuly poke a wire in the passage and possibly blow through a piece of small tubing. Do you see spray exiting?
Hope I answered your questions.
What exactly have you done to try to fix this problem?
Is the backfiring ONLY from the right side pipe?
Is the #4 replacement carb 34 or 36mm? There was some confusion here?
Are you positive the primary and pilot air jets are very clean? They're near the bottom of the carb throat, filter side.
Did you bench synch the carbs in the factory order? I forget the order, but I believe you have to follow a specific order on your model. This is not purely your problem, but it could be a contributor.

 

[J_C]

Hope I answered your questions.

Keith, I owe you a keg of beer for all the help you've given me. I say this from time to time, but I'll reiterate; one of the reasons I bought a GS (as oppossed to any other model) was the generous nature of this board.

Do you see spray exiting?
What exactly have you done to try to fix this problem?
Is the backfiring ONLY from the right side pipe?
Is the #4 replacement carb 34 or 36mm? There was some confusion here?
Are you positive the primary and pilot air jets are very clean? They're near the bottom of the carb throat, filter side.
Did you bench synch the carbs in the factory order? I forget the order, but I believe you have to follow a specific order on your model. This is not purely your problem, but it could be a contributor.

-The carbs had been dipped for several hours and cleaned using the method detailed in the gs garage, though I may have missed the pilot jet hole the first time through. Yes, The spray shoots out the tiny hole into the area next to the slide cylinder. It also sprays out through the air jet. It may have been clogged before but that hole is wide open now, as is the pilot jet.

-To fix it I have attempted the following. Rebuilding (taking all parts out and then all back in), remeasuring float height, checking carb plunger movement, checking for fuel in the boots, checking fuel line, cleaning pilot jet, pilot air jet, pilot hole, main to cross over channel, main jet, needle jet etc, adding new orings (during original rebuild), and checking the diapragm

- Popping is only right pipe, and immediately consistent with the sudden increase in temperature of #4 header

-This is a 34mm carb

-The pilot air jet it clean... primary air jet? Is that the hole without the screw in it?

- The bench synch was done 3,4,2,1. Those were the directions I got off of xs11 for the mikuni carbs. I just received my mercury sticks friday, would these help more experienced people thant I diagnose this issue?


At what point in time do I kind of throw in the towel on this one? The old man wants to take the carbs in, which I am vehemently against, but they might be able to see some thing right off bat that I am not accurately describing. I'm also going to try the old carb body today, crack and all

 

[KEITH KRAUSE]

Primary air jet is located near the bottom of carb throat, filter side, usually the opposite lower "corner" of throat. If pilot air jet is about "5:00", then primary is about "7:00". Primary jets can be "fixed" or removable. In any case, be sure it's clean, though the pilot air jet would be more suspect in your tests.
If you can see spray exit all the tiny pilot circuit bypass holes, near the top of each throttle plate, then you're probably OK, though high compressed air is always best.
A good vacuum tool synch is mandatory, but it has to run well enough to attempt the synch.
Sure sounds like the pilot circuit, but if you're turning the throttle enough to involve the needle circuit, and it's only improved from no fire to back fire, that suggests more carb problems than just the pilot circuit not delivering fuel. Tape your throttle housing and grip and mark for closed and about 1/3 throttle positions. Allow for any slack before the throttle actually opens. Where does the backfire begin? Does opening it up to 1/3 continue the backfire?
I'd still like to see the electrical tested, if possible. I assume that, at least, the plug cap connections and coil terminal connections have been checked for clean and tight?? Plugs new or at least very clean? Gapped?
Installing the old carb would possibly help figure things out. If the old carb works but it's cracked you'll have to try to find a known exact replacement. How have you tried to temp repair the old carb? J/B weld or ? What was the damage to it?
I'm against taking the carb in too, but only because most mechanics aren't good at these CV's. But that doesn't mean all mechanics are that way.
If you CAN get decent results from temping in the old damaged carb, that would certainly suggest you just have something wrong with that replacement carb and we can focus on all the things that it could be.
You're the one doing the work, but I'd probably try the old carb too...if you believe it's repaired enough to make a good test. Don't forget to check it for float level, mixture screw adjustment, etc, before trying it.

 

[KEITH KRAUSE]

One other thing. I checked the factory manual for an '80 GS1000E (BS 34SS carbs) and it says the #3 carb is a master carb. That means #3 shouldn't even have an adjuster on it. Does it?? If no adjuster, the factory order of bench synching is to set #2 first...then #1...then #4. The vacuum tool synch is the same order of course. If you do have an adjuster, then disregard this.
Only extra thing to know is, on ALL CV equipped Suzuki's, with stock intake/exhaust, you must vacuum synch the middle (2 and 3) cylinders a little lower than 1 and 4. I believe about 1/2" lower mercury will be OK. That's with stock intake/exhaust only.
Like I said, this info is for the same carbs apparently, but on a '80 1000. I would think they're physically/mechanically the same. There shouldn't be a difference with how the synch procedure is done. I'd trust it before referring to a Yamaha 1100 article.
Don't know how much a possibly poor bench synch is contributing to your problem, but it's just another thing you can do right and eliminate it as a possibility.
Today is yard work day for me, so I'm outside for several hours. I'll try to check back in around 3:00 if you have any more info or need help.

 

[J_C]

I'll go out and mark the throttle and test beyond 1/3. The plug cap connections have been tested. I'm not exactly sure what the coils look like but I'll see if I can give them a look and perform those electrical tests.

The spark plugs only have about 15 minutes of running on them. I checked the gap before putting them in, and switched #3 and 4 yesterday to ensure they weren;t the problem (The spark plugs worked before the new carb body but just checking to make sure)

The old carb body cracked (hairline crack, not broken) while attempting to remove a seized air screw. I haven't attemped sealing it yet, but I will today with jb weld (Assuming the threads still line up)

The gs1100 does use BS 34SS carbs. #3 does have the idle adjuster on it, though the threads are worn on it so it tends to slip with the spring installed. I took the spring off to bench synch it.

I'm beginning to think I should hold off on the vacuum synch until the pipes are here (they got delayed a week) since I will need to redo it again after it comes anyway.

In the meantime I will see if I can test the 1/3 throttle and try to repair the old body. Thanks Keith!!


Edit: Results:

At idle (Choke): No popping
At idle (no choke): 4th header now heating up (maybe somewhat slowly compared to 1,2,3). Popping intermittent out of right pipe.
1/6 throttle. Popping frequent, increasingly frequent as throttle increases
1/3 throttle. Popping has almost disappeared

This afternoon I will go out for an audio recording. This might help?

 

[J_C]

Here are the audio files. Unfortunately The popping is hard to hear... its more prevalent in the second file.

The files are sequential ( no time lapse) Starting from cold choke. The bogging is when I let the idle too low (Again, no adjust knob). At some point I rev to 1/3 and the pops go away.


http://socal-letsride.com/storage/GS1100L/CIMG0015.WAV
http://socal-letsride.com/storage/GS1100L/CIMG0016.WAV

My uneducated guess says that there is some kind of synch issue with #4 since it won't pilot circuit on choke, but it will when I use the throttle like an adjust knob to 1100 rpms. There must also be some kind of problem with the jet needle.

 

[KEITH KRAUSE]

OK. Heard that, and it wasn't pretty!
My opinion is that's not backfiring...that's the sparkplug or mixture intermittently firing.
Every time you hear a pop, that's the plug spark igniting the mixture. You obviously don't have the correct mixture or correct spark for continuous combustion.
This exact popping can be from a mixture problem, or, poor spark.
If the mixture is wrong, it will only ignite some of the time.
If the spark is poor, it can only ignite a very rich mixture. Once every several cycles, your mixture would collect to the point that a weak spark could ignite it. It should fire every power cycle of course.
I still would like proof that the electrical is good, but you seem convinced it is. While I think so too, I'm just naturally skeptical. I'll forgo the electrical because I want to simplify and just help you. We'll do whatever can be done to find a carb problem and hope it is a carb problem. It does make sense mainly because you're sure the connections are good and that #1 is receiving good spark. So...
It clears up pretty good at 1/3 throttle, anything less creates popping. I also think I heard some fuel starvation in the audio, though you say that could be just you allowing the rpm's to drop too much because of an idle adjuster problem. I have to say it sounds like fuel starvation, NOT you allowing it to drop. Most bikes pick up much quicker when the rpm's drop too low for a moment. Yours sounds like it's really struggling to pick up? Hard to say because I'm not turning the throttle. The fuel starvation thought certainly fits though.
What's interesting is it seems to be improving some? At one time you didn't see any fuel wetting the throttle plate at #4. I assume you did some more cleaning to the pilot circuit? Or is the improvement mostly because you're turning the throttle more? What color is the #4 plug after a minute or so of running? Only problem with a plug read here is because the choke may/will darken the plug and you may need more time for the plug to show a true color that's doesn't have any choke effect. It would be nice to compare the plug to the others though, in any case. They're all under the same start up conditions.
The more we talk about these carbs, the more it seems is wrong with them. First the idle adjuster, now the synch mechanism. I have to wonder what else may be wrong? A poorly synched throttle plate means incorrect vacuum. Too much or too little, as compared with the others, will cause major problems. In your case, it sounds like you don't have enough vacuum to draw sufficient fuel through the pilot jet and to a lesser extent, the jet needle. If you're POSITIVE the pilot circuit and jet needle/main circuit are clear/clean and the jets are identical to the other carbs and the floats are adjusted the same, then that would eliminate any fuel flow question. That would mean the only reason fuel can't be drawn up through the pilots passages/jets, is because of poor vacuum. Poor vacuum is most commonly a throttle plate issue. Poor vacuum can also be a bad or unseated diaphragm or spring problem but you say the diaphragm assembly is good. Besides, a torn diaphragm generally doesn't accept ANY throttle beyond idle. Poor vacuum could also be an intake leak, but without reading back, you say there are no leaks, correct?
So we're looking at a vacuum problem it appears. Opening the throttle increases vacuum and as you open the throttle the bike runs better and better.
So, knowing you have a problem with the synch adjuster and it appears the other things are checked, it does sound like the synch or throttle plate is the problem. How does the #4 plate compare (visually) to the others.
It can't be opening "behind" or "ahead" of the others. A very tiny amount is acceptable for an eyeball bench synch, but not any more than that. It also has to operate smoothly and the same as the others.
It's hard to watch the plates under running conditions because these CV equipped bikes run badly with the air box off. You may have to wait to see the true vacuum you have when you get the synch tool.
Problem is, your bike may not run well enough to synch it. But it might. You'll have to be careful of mercury rising too much if you have to attempt a synch in this condition. But maybe we'll find the problem before that.
Let me know what you try. Trying the original carb will be interesting, if you do.
Be patient. If you're giving us good/complete info, I think you're getting there.

 

[J_C]

Thank you Keith. The frusteration from yesterday has subsided; I'm just glad I have great help! I agree that the electrical should be tested, I just didn;t have time to learn how to do it today When I get back on Friday I will start giving it a once over. (Bike lives in Burbank, I travel to Houston every week for work)

There do seem to be minor improvements every day, though God knows what I'm doing to get them. I did clean the pilot circuit extenively so that may have been a step in the right direction. I don't think it was just turning the throttle. In fact, I have it idling on its own now after adding some thread tape to the knob threads.

I listened to check whether the popping was cyclical or random, and it definetely seemed more random. I think a key indicator here is the plug color. I ran it on choke for about 45 seconds, then let it idle between 1100 and 1400 for about 3 minutes. After that I checked all four plugs. 1,2 & 3 all were a light off-white gray, while #4 was almost completely black. What's causing that I don't know.

That would mean the only reason fuel can't be drawn up through the pilots passages/jets, is because of poor vacuum. Poor vacuum is most commonly a throttle plate issue.

I think this just might be the case. I will need to wait until next week to perform the carb synch with the mercury sticks to see if that might shed some light.

Does the plug color tell us anything?


Thanks again, I'll have to bring you a friendship cactus or something for your yard :-D