Hi guys, I'd appreciate if any of you could throw light on this situation...
I picked up a project first-gen GS a couple of months ago, to fix up as a starter bike for a friend, that had a lean-running condition, so I figured it was a simple carburetor related issue. To save the trouble of dealing with the airbox, I immediately ordered a KN lunchbox and the recommended jet settings for sea level, which I have read of several others having success with at my elevation:
pilot 40
main 140
washers 1
turns 2.5
Tried stacking up to 4 washers under the needles. Same symptoms.
Jetting and meticulously cleaning the carbs several times did nothing, so I replaced the carbs. Same symptoms.
Adjusted valves, read on this site that over-tightened exhaust valves can give those symptoms, and I found that they had the infamous too-tight for too-long issue where they actually damage the head itself, so I just got finished replacing the head with a very clean one that is proven not to leak, and all valves are close to the maximum allowed within spec. Intake are at .006 and exhaust are at .012.
I'm using a gas bottle with the tank off, so fuel delivery or hose/filter blockage is not a factor.
I'd appreciate if anybody had any experience with GS motors that behaved similar to this - really not sure what else to possibly try at this point...
Thanks for reading.
EDIT: I feel like I didn't adequately described the lean condition - the bike starts and idles just fine at 1500 or thereabouts. As soon as throttle is even mildly blipped, it shoots up to 5-6k and will under no circumstances return to idle rpms unless it is forced down by engaging the clutch and essentially bogging the engine until it returns to idle speed, or removing the lunchbox and covering the air intakes.
Check your float height?
Ah, I forgot to post that I had checked them. They are within spec.
Ah, ok. The edit you added makes it sound like a wandering idle. What year is the bike, and how many miles? Most wandering idles stem from either bad intake boots (between the carbs and engine) or intake boot orings.
Just checking: have your carbs been vacuum synchronized?
Have you tried 150 mains? I think that is the typical for a lunchbox. Also, check the fuel level in the bowls with a clear tube from the drain. The level in the bowl should be right at the bowl gasket. Either the float needles or a malfunctioning petcock can limit the fuel level in the bowls.
Rich makes a good point with the intake boots too, if your symptoms persist with new carbs, I'd look to the boots for air leaks.
Quote from: Big Rich on June 29, 2014, 10:00:26 AM
Ah, ok. The edit you added makes it sound like a wandering idle. What year is the bike, and how many miles? Most wandering idles stem from either bad intake boots (between the carbs and engine) or intake boot orings.
Just checking: have your carbs been vacuum synchronized?
Thanks for the reply. The synch on the carbs is good. The bottom end has about 35k, mileage on the head is unknown. We sprayed carb cleaner liberally around the intake boots to no effect, even went out and tried it again just now, so I don't think air is getting in from there. The rubber on the boots is in pretty decent shape...
Quote from: bombsquad83 on June 29, 2014, 10:07:17 AM
Have you tried 150 mains? I think that is the typical for a lunchbox. Also, check the fuel level in the bowls with a clear tube from the drain. The level in the bowl should be right at the bowl gasket. Either the float needles or a malfunctioning petcock can limit the fuel level in the bowls.
Rich makes a good point with the intake boots too, if your symptoms persist with new carbs, I'd look to the boots for air leaks.
We tried some 147.5s that we had lying around, so a considerable step up, with 0 change in behavior, but actually now that I type that, that was before the head swap. That was one thing I forgot to try all over again with the new head. Though I made sure to go through about 70 pages of the carb settings/elevation thread so that I could get a handful of people who verified no running issues with my current settings at my elevation, so I still doubt that's the issue, but I have to check again, now...
I have not checked the fuel level in the bowls. It is possible the petcock is malfunctioning. Maybe I'll just bypass the petcock completely and see how that does, too.
Quote from: bombsquad83 on June 29, 2014, 10:07:17 AM
Have you tried 150 mains? I think that is the typical for a lunchbox. Also, check the fuel level in the bowls with a clear tube from the drain. The level in the bowl should be right at the bowl gasket. Either the float needles or a malfunctioning petcock can limit the fuel level in the bowls.
Rich makes a good point with the intake boots too, if your symptoms persist with new carbs, I'd look to the boots for air leaks.
I bypassed the petcock with the same results, and realized that the issue is occurring long before the main jets are used at all, so I've kind of ruled out swapping the mains for 150s. Main jets shouldn't be used at 2200 rpm at all, and that's about where the RPMs suddenly take off...
Just realized too that there's now an oil leak coming from the base gasket now. :mad: It more than likely worked itself loose when I was swapping the head last night. :technical:
You could have an air leak in the head gasket. Also, forgive me for asking, but have you tried turning down your idle speed? Remember you should need some choke until the engine is warmed up, so don't set your idle speed until the engine is up to operating temp.
Quote from: bombsquad83 on June 29, 2014, 10:51:10 AM
You could have an air leak in the head gasket.
When seating the head gasket, I liberally sprayed some of that permatex copper sealant spray on both sides of the mating surface, so I really doubt that's it. That's the stuff many people use, including myself, on the Suzuki Bandits, with great results.
Quote from: bombsquad83 on June 29, 2014, 10:51:10 AM
Also, forgive me for asking, but have you tried turning down your idle speed?
Yes, yes I have. You are forgiven. :wink:
Just really hoping somebody has been through this before, me and a friend have pored over every thread on this forum and others about the symptoms, and still, nothing's coming up.... :dunno_black:
This is a head scratcher...
Have you done a compression test? Double checked valve timing? If those are both good, then it has to be something with the carbs or intake boots.
Quote from: bombsquad83 on June 29, 2014, 01:23:48 PM
This is a head scratcher...
Have you done a compression test? Double checked valve timing? If those are both good, then it has to be something with the carbs or intake boots.
I have not done a compression test yet, but I've been looking for an excuse to test out my recently acquired compression tool.
By valve timing, do you mean that the cams are in the correct position in correlation to the crank? The marks on the cam lobes were facing one another totally horizontal at TDC when I snugged everything down, and I did a few dry turns of the engine with the spark plugs out to make sure everything was moving nicely and there weren't any collisions before I sealed everything up. I've done the same procedure on other bikes several times, and I'm comfortable with it.
As carbs go, 2 sets of carbs, and 2 sets of intake boots, with liberal spraying of carb cleaner around those areas while running to check for leaks via engine surge have rendered nothing. I'm really ready to set the thing on fire and throw it out on the lawn. It doesn't deserve THIS much attention.
could it be as simple as missing the vacuum port orings?
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Ace, this is an older style carb and takes different sizes then the newer carbs for the lunchbox filter.
It's not a bad idea to return to stock and see what happens though...
Check the orings on the vacuum ports, and that the vacuum ports are properly capped of course, but since you said it was two sets of carbs I'm guessing that's not it. What about your vacuum line to your petcock? You said you were running off a bottle, so did you make sure to adequately cap off the vacuum port that goes to the petcock? The vacuum line or the petcock diaphragm could be leaking, so remove them and cap it off at the carb.
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Quote from: ace50 on June 30, 2014, 05:16:33 AM
So when he said 'first-gen GS' is that just the 2 circuit carbs or more than that?
First gen had the 2-circuit carbs. Not sure why you said the jetting was too rich. The wiki jetting chart has at least a 140 main jet for a lunchbox filter.
http://wiki.gstwins.com/index.php?n=Upgrades.Rejetting
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Hey guys. The o rings are fine under the carb caps. As far as the vacuum line I was plugging it during testing to see if it would make a difference, and it didn't. Really can't see what I could've missed at this point. It's pretty bizarre.
It was doing the same exact stuff with the air box and stock settings, and that thing is so hard to wrestle in and out and get connected that I went to a lunch box just for the ease of troubleshooting.
Okay, I'll admit I quickly skimmed through this thread... but, I remember a post from adidasguy awhile back that involved a lean issue... went through the whole charade of swapping carbs, heads, etc... everything anyone has thought of basically... and it finally turned out to be an issue of the timing... it was one tooth off
- Bboy
http://img.photobucket.com/albums/v443/jcp8832/gs500signalgenerators_zps2134172a.jpg
I have had a similar or wll identical symptoms.
i tackled it head on and between head and carb manifold smeared high temp silicone sealant(automotive grade).
then the same for carbs to manifold and airbox to carb.
aswell as synking the carbs that did the trick, although it can still happen if the idle is too high.
id get the bike upto temp and reduce the idle to try and bring it back down.
could be a case of only one cylinder is firing untill warm when both kick in.