need CV carb exPERT

[nert]

1982 GS1100glz Stock, except Dyna ignition and K&N air filter in the stock air box. Carbs have been gone through. Starts in a milly second, and is NOT cold blooded. Idles like a rock at even 800 rpm. Good equal compression across. Valves properly adjusted. I don't push it hard. 48 mpg.

These symptoms have always been there, even before the carb cleanup) Has always been rough going through the 3000 to 4000 rpm range. Does not accelerate smooth or freely, kinda "labors" and seems noisy. Above 4K is smooth, cruising is smooth, acceleration gets stronger above 5k but not overly exciting.

I installed rebuild kits using the correct jet numbers. Anal that I am, and understanding that float weight can vary and the preload springs in the needle valves can vary, I installed a clear window in a spare fuel bowl and adjusted fuel height evenly and to spec across the 4 carburetors. NOT to my surprise actual fuel float levels varies among carburetors. After reading CV Carb Tuning several times, I decided to lower the fuel level. ( I always believed it to be a little fuel rich) I raised the current float levels 1.2mm each with out doing the fuel bowl window thing to lower the fuel level. There was a positive affect on performance. Not completely fixed, but better

Now that I have been riding in 34 to 64? temps the problem is almost non-existent. Engine is much quieter, accelerates more freely, and a greater joy to ride. (I suspect some of the quietness has to do with the colder oil, but I also believe combustion noises are quieter.) Still not cold blooded, which I have read is normal for these bikes. Choke to start, easily drive off at less than half choke, less than a mile @ under 30 mph choke all off. And that?s a 40?. By the way, the fuel mixture screws are only out by a half turn, any more and idle quality suffers. No the choke circuit is not leaking or partially on. Improved performance in the cold, I think only supports my feeling of rich mixture.

I like to ride when its warm out, but I like the way the engine runs when its cold out. I am beating my head on a wall with this. I am a stickler for detail and don?t usually miss too much, if anything at all. Marked a piece of tape on the throttle. Seems I barely ever go beyond a quarter throttle. Most of this poor performance is in the one eighth throttle range. Sorry for the very long post. Thanks for any suggestions.

[Jethro]

At 2800 RPM (if I remember correctly), your timing advancer kicks in. Check that it is lubed and the springs are not broken. I had the same problem with my 1100E and chased carb problems for about a year. Had a broken advancer spring.

[nert]

The stock unit was electronic advance as well as the Dyna set up. Checking with a timing light, advance does work. I have tried (2) of the Dyna built in advance curves for comparison. (2) curves are for 2 valve engines, and 2 curves are for 4 valve engines, and a couple of curves are retard mode for NOX? Doesn't seem to make a differance which of the (2) curves i use.

thanks

[IanFrancisco]

Re: need CV carb exPERT

These symptoms have always been there, even before the carb cleanup) Has always been rough going through the 3000 to 4000 rpm range. Does not accelerate smooth or freely, kinda "labors" and seems noisy. Above 4K is smooth, cruising is smooth, acceleration gets stronger above 5k but not overly exciting.

Now that I have been riding in 34 to 64? temps the problem is almost non-existent. Engine is much quieter, accelerates more freely, and a greater joy to ride. (I suspect some of the quietness has to do with the colder oil, but I also believe combustion noises are quieter.) Still not cold blooded, which I have read is normal for these bikes. Choke to start, easily drive off at less than half choke, less than a mile @ under 30 mph choke all off. And that?s a 40?. By the way, the fuel mixture screws are only out by a half turn, any more and idle quality suffers. No the choke circuit is not leaking or partially on. Improved performance in the cold, I think only supports my feeling of rich mixture.

I like to ride when its warm out, but I like the way the engine runs when its cold out. I am beating my head on a wall with this. I am a stickler for detail and don?t usually miss too much, if anything at all. Marked a piece of tape on the throttle. Seems I barely ever go beyond a quarter throttle. Most of this poor performance is in the one eighth throttle range. Sorry for the very long post. Thanks for any suggestions.

The pilot circuit affects 0 to 1/3 throttle openings as well as idle. At only 1/2 turn out on the pilot screws I would think that not enough fuel is getting into the motor in that throttle postion range. Or the mix is too lean which would support the fact that the bike runs better at colder temps. Higher temps would exacerbate the lean condition. I think that most guys run their pilot screws at 1.5 to 2.5 turns out from lightly seated. You also might consider adjusting the needles, although that is supposed to affect only 1/3 to 2/3 throttle postions. Plug chop testing should tell you something about the mixture at small throttle openings. Has to be done at the side of the road though, so be safe.

I read somewhere that the hardest two things to get the carbs to do is 1)idle and 2) run wide open. You seem to have the idle working but at abnormally small pilot screw settings. Does the bike run well wide open?

[nert]

wide open is good. its not scarry, but that good be subjective. I always thought that cold air will help a RICH fuel mixture because 1) the air is more dense and gives a greater air volume the already present fuel. and 2) cold tends to cause fuel to collect/condense fuel on the intake track, cylinder walls etc. and not atomize very well, THUS the need for a choke when its cold. In addition, applying choke during this troubled rpm range does not help. too much choke makes the problem crippling. The small idle screw adjustment also tells me there is a rich condition, because i need to limit the fuel so much to get a good idle. I believs a warm engine can more easily handle a lean condition than a cold engine for the reasons stated above. Althogh a lean hot engine can also cause mechanical damage.
I guess i need to perform plug chop? What do i do, run at 1/8 throttle in what gear? for how long? then kill and pull?

thank you

[IanFrancisco]

I think wide open throttle on an 1100 should give you some pretty serious acceleration. If you don't get up to 100mph+ speeds in a hurry I think you have not yet "released the beast"! As far as the lean/rich concept I think you have it backwards. Many bikes won't start when cold on a lean mix. The choke enrichens the mixture allowing the bike to start. A cold running motor will tolerate a lean mix better than when it is running hot. The heat in the motor makes for a more complete burn of the mix and if hot enough will cause detonation. To much choke will kill/cripple an already warm motor, it enrichens way too much. We're talking fine-tuning here. Possibly your mains and needles are causing a rich mix which you have to over-compensate for by running the pilots at only 0.5 turns out from fully seated. None of the guys here run their pilots that far closed. Use the search feature. Tons of stuff on setting up four-cyl. carbs. Note that I'm don't own a four cylinder bike so I can't be considered an expert, but I have been reading up on this forum and elsewhere for several years.

Different guys have different techniques for doing the plug shop but the basics are to run the bike at the throttle position you want to test with a warm motor for at least 15 seconds. Has to be in gear and moving. Then pull the clutch and cut the motor without closing the throttle. Coast to a stop and pull the plugs.

Another thing I just thought of is bowl vent lines. Someone mentioned having to cut them to a certain length to reduce turbulence in the bowls. Again do a search. There's tons of info here and many guys have been down the same road you're on at the moment. Best wishes getting the bike dialed in!

[nert]

I think you just said, what i had said. We do agree. And my bike does run good cold, indicating a richer mixture to begin with, I need just little choke once it started. and it starte immediatly. And when its warm it don't run too good. The first phase (lowering the fuel level, leaner mixture) did improve the performance.
thanks again

[KEITH KRAUSE]

nert, you're correct about the rich/lean discussion.

[KEITH KRAUSE]

Have you vacuum synched the carbs? Your problem description fits unbalanced carbs. A higher vacuum at one or more carbs would make that cylinder run richer than the others and cause poor performance in a limited rpm range. Colder weather would compensate for the richer level(s) and performance would improve without necessarily having an adverse effect on the "leaner" carbs/levels.
Before the synch, warm the bike up and set those mixture screws for highest rpm and re-set idle to about 1,000 rpm's.
Our bikes always make more power with cooler temps. But your description shows a problem, not just more power at colder temps.
Check all the basic stuff first (carb synch), before troubleshooting.

[KEITH KRAUSE]

By the way, just to confuse you more, your mixture screws should be set around 1 1/2 to 2 1/2 turns out, especially with the K&N filter.
Having them set at 1/2 turn to achieve best idle actually suggests a lean/small/plugged pilot jet.
Don't look at the small mixture screw adjustment as compensation for a rich condition. Consider that the mixture screws job is to ASSIST the pilot jet. It does this through a secondary fuel passage and allows fine tuning for each cylinder. If the pilot jet is too small, then best rpm may be achieved almost as soon as the screw is unseated. The too small pilot jet still controls most of the fuel flow but is obviously limited. Turning the mixture screw further will not help in this situation because its fuel flow ability is even less than the pilot jet.
Have you verified the correct stock pilot jets, air jets? Maybe a PO has made incorrect changes?

[nert]

Keith
The BS34SS carbs i have call for a #40 Pilot Jet and a #170 Pilot AIR Jet. That is what is installed. Having read your post and studing the Slow System fuel diagram in the Suzuki Shop manual, It seems to me the idle/slow speed fuel misture is really determined by the Pilot Jet and the Pilot Air Jet. It appears the Pilot Screw can add to or remove amounts of already mixed gasoline and air, "fuel mixture", as needed, based on the amount of just air passing through the throttle plate. The amount of screw needed may well be determined by the amount of throttle plate opening.

My guess is that, If i open the Pilot screws to 1.5 turns, my idle speed would drop, i would then have to increase the throttle plate opening to achieve desired idle speed. In reality, i could have a same "specific" idle speed, one with little throttle plate and little Pilot Screw, or one with greater Pilot Screw and greater throttle opening. Yet the "adjusted" fuel mixture volume would be overall greater for the latter. Am i understanding this correctly?

I Sync the carbs (1) a year, begining the start of spring riding season. I have a Morgan CarbTune. The most difficult part of the sync is the set screw and lock nut, as it it easy to foul the setting once the lock nut is tighten. I have developed a pretty simple carburetor modification to provide tension to the Synchronizer screw, eliminating the jam nut for the Synchronizer screw. Adjustment is performed more easily and more accuratly. I have retested the sync to be sure my design has held up. ( i am most happy with the results). I have modified several carb sets on other Mikuni banks with successful results.

In addition, i sync the carbs with a throttle lock (cruise control) holding the specified RPM instead of the idle speed screw, as i believe the throttle held speed is more appropriate for the procedure, since that is how the throttle is operated. I think the idle speed screw may slightly "alter" the dynamics of throttle position since it applies a force from a differant direction. How real or perceived that may be, i can't see any error being imposed by using a throttle lock to hold the sync RPM.

thanks

[IanFrancisco]

Keith


My guess is that, If i open the Pilot screws to 1.5 turns, my idle speed would drop, i would then have to increase the throttle plate opening to achieve desired idle speed. In reality, i could have a same "specific" idle speed, one with little throttle plate and little Pilot Screw, or one with greater Pilot Screw and greater throttle opening. Yet the "adjusted" fuel mixture volume would be overall greater for the latter. Am i understanding this correctly?

That's not how it worked on my bike. When I opened the pilot screws up to 2.5 turns out from 1.5 turns out, allowing more mix thru, the idle went up and I had to back off the throttle stop screw to get the idle back down to where I wanted it. The reason for doing this was that at 1.5 turns out the throttle stop screw was in far enough (butterflies open far enough) to cause the motor to take some time when the throttle was closed to drop from 2k rpm to 1k rpm. I thought I had a sticky slide or something but setting the pilot screws to 2.5 turns out and backing off the throttle stop screw resolved all that. I now have a rock solid idle even when stone cold. I don't even need the choke with ambient temps over 60F. I use my throttle lock to set the idle up a little higher while I gear up. I also have the BS34SS carbs, but only two of them.

[KEITH KRAUSE]

Well, you say the compression, valves, ignition, carb synch, etc, are good. The air jets/pilot jets are stock.
Your bike is showing rich mixture problems. Your acceleration description suggests a rich mixture and as the bike and outside temps heat up, the mixture richens. Hotter temps and a hot motor is a richer condition than cooler temps and a motor still warming up. Visit any good jetting website and they'll tell you if performance suffers as the bike heats up, you're rich, excluding other problems such as a weak spark.
But, if everything was checked and in good tune, your bike should run a little lean if anything due to the K&N and the fact that your model came a little lean from the factory. Also, the mixture screws can vary from the factory but are generally 1 1/2 to 2 turns out on a totally stock bike. 1/2 turn out on the mixture screws also suggest a lean condition effecting their operation. You also feel the bike ran better with what I'm assuming is a lower than factory recommended float level.
So we have mixed signals. You say the bike has always ran this way, suggesting you inherited this problem? It didn't run well and then develop this later. You most likely have 2 problems that are causing these "rich and lean" problems.
I'll say what I would do if the bike were here and by going on your info.
The K&N requires oiling, with K&N filter oil only. Be sure it's clean and oiled correctly. Hopefully, it was always cleaned and rinsed from the inside out.
Re-clean the carbs completely. Replace any o-rings not in supple condition. Re-adjust the float levels to the factory setting and be sure you're taking the measurement at the correct part of the float. This is the top of the float body, not the arm section (common mistake by some).
Using a detailed manual, verify all parts are there and in correct assembly order, such as the jet needle assembly. Verify the mixture screws are the correct ones if you can. A PO could have made a change?
Turn the mixture screws to 1 1/2 turns to begin.
Bench synch and then vacuum synch again, AFTER adjusting the mixture screws for best idle (fully warmed up motor). Set idle to about 1,000 rpm's.

[nert]

Keith, thanks
spark is good and hot
Pilot screws are from a kit, as are the o-rings new and plyable. did a rebuild beginning of season. Float levels are measured correctly. I think initially setting the fuel "level" method, the fuel level was to the high side of spec.
When i lowered the fuel level (raised the floats) they measured. 22.4, 23.6, 22.7, 22.9. There is a 2.0mm tolerance from the mean 22.4 Still kind of where they should be.
My variation in height is due to the (i think preffered) method of setting fuel level as opposed to float height. (compensating for variations in float weight and needle and seat unloader spring, etc.). But i did measure the height as a curiosity. LAst night i set the screws at (2) turns out and re-adjusted idle speed to 950. Ran better in the troubled RPM range (60' to 50' ambient) 30 mile ride home. This morning (38' to 50' ambient temperature) still ran very good. At the end of the 30 miles, still pretty good, but was better for the first 15 miles or so. I have not service the K&N since i installed it about 8K ago.
One last question. From the now initial (2) turns out, would turning in the screw deliver more or less fuel through the troubled RPM range.?
Thank you again for sticking with this post.
vic

[Road_Clam]

Keith, thanks
spark is good and hot
Pilot screws are from a kit, as are the o-rings new and plyable. did a rebuild beginning of season. Float levels are measured correctly. I think initially setting the fuel "level" method, the fuel level was to the high side of spec.
When i lowered the fuel level (raised the floats) they measured. 22.4, 23.6, 22.7, 22.9. There is a 2.0mm tolerance from the mean 22.4 Still kind of where they should be.
My variation in height is due to the (i think preffered) method of setting fuel level as opposed to float height. (compensating for variations in float weight and needle and seat unloader spring, etc.). But i did measure the height as a curiosity. LAst night i set the screws at (2) turns out and re-adjusted idle speed to 950. Ran better in the troubled RPM range (60' to 50' ambient) 30 mile ride home. This morning (38' to 50' ambient temperature) still ran very good. At the end of the 30 miles, still pretty good, but was better for the first 15 miles or so. I have not service the K&N since i installed it about 8K ago.
One last question. From the now initial (2) turns out, would turning in the screw deliver more or less fuel through the troubled RPM range.?
Thank you again for sticking with this post.
vic

Another method I use to give me an idea of whats going on as far as combustion, is to measure the temps of the exhaust header pipes. I have a cheap Radio Shack infared temp meter. This is a super quick way to tell a poor firing cylinder, a lean cyl, overly rich, and so on. It won't tell you exactly what the problem is but it isolates an "off" cylinder(s). Carbs all synched dead nuts will yield temps within 4 degrees of each other in my experience.

Rich