If not jetting, then what?

[Guest]

Dear all,

I have been struggling for a while with the carbs trying to get the GS850 to behave.

It runs OK when cold and with the choke on. It hangs in the RPM's instead of dropping down to idle when the throttle is released. When it gets warm, it begins to run very poorly. It won’t stay stable in idle, and I have to rev it every 15 seconds to keep it from going out. There is many backfires when I am driving, and on my last trip it suddenly rose in idle RPM to around 3500, but almost died when I tried to run it.

I have an Air Fuel Ratio meter connected to the bike, and it reads slightly rich (AFR around 12.5 - 13.0) even though some of the symptoms above usually are found in the "your bike is lean" pile.

I am therefore considering if there are other things that might cause the above mentioned issues, and that I should look into before trying to dial in the carburetors.

Can you think of anything else that could result in the conditions above? If you also have a method for testing if your issues is causing my troubles, then that would be great.

Thanks in advance.

Best regards

Michael

[Big T]

Have you adjusted your valves?
Cleaned your carbs?
Synced your carbs?

https://www.thegsresources.com/_foru...ers-CLICK-HERE!!

https://www.thegsresources.com/_forum/showthread.php?171846-Top-10-Newbie-Mistakes&highlight=top%20newbie%20mistakes

http://members.dslextreme.com/users/bikecliff/

[BigD_83]

Hi Michael,

it does sound more like lean condition symptoms mixed with some rich, which could indicate some wholescale carburetor cleanliness issues, as BigT suggested.

Going back to basics and establishing a baseline by cleaning the carburetors and adjusting the valves would be a really good place to start.

[TxGSrider]

I have a wideband set up on my gs1100, and it's a terrific tool for tuning. It's weak point is that it takes an average a/f measurement for all four cylinders, and that can sometimes drive you a little crazy. An example is, I was tuning one of the other member's bike and the readings showed rich at idle and mid-range. We leaned the fuel screws and lowered the needles. The a/f got better but the bike ran worse. Turns out one of the carbs had a float needle issue and that 1 cylinder made the a/f rich, and by trying to correct the a/f we made the other 3 cylinders too lean. So be sure all the carbs are clean and adjusted and there aren't any air leaks before you start taking readings.

[DKGS850]

Dear all,

I think I am getting closer.

I checked the synchronization (all good), the valves (within spec) and I knew the carbs were clean, as I had taken them apart a billion times to rejet. Never the less I decided to take the carbs apart and clean every nook and cranny, while rejetting.... and something helped. It now runs, but with a lot of back popping and coughing out through the air filters.
I tried to adjust the pilot air screw, and it had an effect on cylinders 1 to 3, and zero effect on cylinder 4.
As far as I know that points towards an air leak on cylinder 4, so my next move will be checking the carbs and boots by spraying some starter spray to see if the idle changes.
I have also heard about leaks in the exhaust headers causing trouble.
How do you check if your exhaust headers leak?
Any place else where you typically see air leaks on GS850 and VM26SS carbs?

Best regards

Michael

[BigD_83]

Dear all,

I think I am getting closer.

I checked the synchronization (all good), the valves (within spec) and I knew the carbs were clean, as I had taken them apart a billion times to rejet. Never the less I decided to take the carbs apart and clean every nook and cranny, while rejetting.... and something helped. It now runs, but with a lot of back popping and coughing out through the air filters.
I tried to adjust the pilot air screw, and it had an effect on cylinders 1 to 3, and zero effect on cylinder 4.
As far as I know that points towards an air leak on cylinder 4, so my next move will be checking the carbs and boots by spraying some starter spray to see if the idle changes.
I have also heard about leaks in the exhaust headers causing trouble.
How do you check if your exhaust headers leak?
Any place else where you typically see air leaks on GS850 and VM26SS carbs?

Best regards

Michael

I don't want to beat on the "clean carbs" drum too much, but I understand your phrase "every nook and cranny" meaning the visible parts of the carburetor. Can you set us at ease and describe exactly what you are doing to clean the carbs?

[Suzuki Mad]

I've just shoved a set of carbs through an ultrasonic cleaner. First time ever for me.

As I couldnt get No 1 needle out I cleaned it anyway. When I look down through there 2 and 4 appear to be a larger hole, no3 is smaller and No 1 I can hardly see down through it.

Maybe, and only as a maybe you are having the same issue with your No 3 carb.

I'm going to have to re clean these carbs and make sure that all the ports are clear.

I say that, the guy that showed me and who's kit I am borrowing, did my GS1000 carbs and they are working really well. The only difference between the two jobs was that Pilot needle being out and the 2 carbs pilot needles holes being different sizes.

Just a suggestion.

[LAB3]

If you get to the point where you're sure the carbs are properly cleaned i'd start looking into your ignition. Misfiring when hot seems to be a sign of ignition to me, have you checked or replaced your spark plug caps?

[DKGS850]

Dear all,

When I did "every nook and cranny" on the carbs, it was an internal cleaning. Took them totally apart. Removed all jets, screws, choke plungers (more or less everything brass) and blasted every channel with some aerosol carb cleaner. I am sure that an ultrasonic cleanse would be better, but I don't have one readily available. Perhaps that should be one of the future investments.

As for the ignition: I don't think that is the problem. The bike is fitted with brand new Dyna coils, new spark plug wires and caps, and the ignition timing is a brand new Dynatec electronic ignition as well.

Ill be continuing my trial and error search today. Swapping some jets, Colortuning all cylinders and also checking for vacuum leaks. I understand that the preferred M.O. for vacuum leaks is spraying the intake boots with some starter spray and look for an increase in RPM.
Any other weak spots, besides the intake rubbers between the carbs and the cylinders that I should be aware of?

Best regards

Michael

[LAB3]

I've done the "Half fast" carb cleaning before and never ended up with the kind of performance I got after a long soak. If you're going to take the carbs off again make it for the last time and soak the carb bodies overnight in solvent!

[BigD_83]

I agree with LAB3. Blasting the carbs with aerosol is great for finishing them up, but isn't a true substitute for a 24h carb dip. Ultrasonic isn't necessary either, unless you've got some long-standing issue. If that was the case, you'd see far worse performance than described.

Still, if you are blasting the carbs in all the right places and you are getting good mist at the other end, carb cleanliness may not be the issue.

While your electrical components maybe in great shape, have you had a chance to measure the voltages in and out of the coils?


When you start up from cold, do all cylinders fire up right away, or does #4 take awhile?

[fastbysuzuki]

If you have been just using carb spray then I would recommend striping and dipping the carbs and while you are there put in new orings examine the inlet rubbers and renew the orings that fit between the cylinder head and the inlet rubbers
get all the orings here http://www.cycleorings.com/.

carb strip/dip here. http://zeus.mtsac.edu/~cliff/storage...d_Tutorial.pdf

[KEITH KRAUSE]

Unstable idle and spitting out of the filters are classic lean issues. I assume you are running pod filters? What brand? Do you have a quality aftermarket exhaust? Did you re-jet? Any other mod's?
Don't bother to spray the intake manifolds. You can often miss the leak. Since you've had the carbs off many times and know the routine, remove the intake manifolds and inspect the o-rings. I would order some o-rings from Robert Barr or ? and just replace them, provided the manifolds themselves are in good condition. Apply a coat of hi-temp grease to the o-rings. Get some Allen head bolts for the manifolds and torque to about 9-10 ft lbs. Be certain the manifold clamps are applying enough torque to properly seal. The thin clamps can lose the ability to squeeze the manifold and intake leaks can result with change of temp's. If you're running pods then remove the two float bowl vent lines and leave the ports open to breath easier. Be sure the floats are adjusted correctly. Float needles valves and seats should never be mixed. Always replace the float needle valves gasket to avoid leaking. All carb o-rings need to be in good condition. Before and after a vacuum synch, with engine at full running temp, adjust the side air screws using the highest rpm method and use 1,000 rpm's as a base idle before adjusting each carb. If any carb doesn't respond to the side air screw adjustments and you're using 1,000 rpm's as a base idle, then that carb has blocked passages or some other issue. Be sure the pods are oiled correctly if they are K&N's for example. Be sure the throttle cables have correct slack and the return cable works even when the bars are turned to one side.
These are all basics that are needed for any bike. I can only assume the carbs are now completely clean. Valve clearances adjusted as you said. Ignition and spark are good you said. Have you verified compression on all cylinders and no issue with imbalance? if so, then I have to guess your jetting is not right.

[DKGS850]

Dear all,

Thanks a lot for all your replies. This is the general update

I went and bought a 10 liter ultrasonic cleaner, and gave the carbs a good cleanse in water with a dash of house hold all round cleaner added to the water. I could see that it had an effect as the water became very cloudy, but I cant tell if the ultrasonic cleanse unclogged anything. When I tested the carbs afterwards, I was now cylinder 1 instead of cylinder 4 that was colder than the other 3, which leads me to one of the following conclusions:

1. Carb tuning is 0% predictable technology and 100% witchcraft, or
2. I have an intake leak between the carbs and the intake manifold, coming from a slightly crooked mounting of the carbs.

I am leaning towards option 2, but I haven't dismissed option 1 entirely.

My next task will be taking the carbs apart.... again. Giving them a even more thorough ultrasonic cleanse. After they are squeaky clean, Ill be mounting them as parallel to the engine block as possible.

@LAB3: I have been unable to find non aerosol carb cleaner in Denmark, but in a Danish forum, a 50/50 mixture of "rubbing alcohol" and benzine, have been suggested as an alternative. Which solvents have you been using for your over night soaks?

@BigD: I have not measured the spark, but is very visible. Either with a spark tester, or with my ColorTune.

@FastbySuzuki. I have a brand new set of orings from Orings Are Us

@Keith Krause. Thank you very much for a highly detailed "To Do" list. I will be going through this, and ticking them off one by one, next weekend. As for your questions. I am running PODS. I think the brand is EMGO, so not quite K&N, but not too shabby either. I have a 4 in 1 Sebring exhaust on the bike, with a no name muffler on it. The carbs are currently jetted with a 15 pilot and a 110 main jet.

BR Michael

[KiwiGriff]

Nice to see your progress Michael. I'm about to undertake the same process with my GS1000G. Still waiting for my JIS screwdrivers and new O-ring kit to arrive. But I'm hopeful that it's actually not witchcraft! Good on ya.
Cheers, Griff