Do GS1100s naturally run rough at low speed?

[rapidray]

You need to replace the orings in the 4 float needle brass housings. That or you have a bad float needle or screwed up float height. 95% of the time it is the orings. Pull the needle housings, remove the old orings, clean the housings, install new orings & grease the orings before re-installing the needle seat housings.
Ray.

[Paul.S]

Cool I will go ahead and just order all the faskets and o-rings for these carbs and totally rebuild them. Hopefully that will help. Thanks alot for all the advice!

[chef1366]

Are you using a vacuum petcock?
Be careful building that 82 crank.

[CivilRock]

I know the least of all the guys that have posted ideas here, but as I was reading I was going to suggest carb sync and then float valve fixing. (which got suggested as I read).

My RS38's also come with instructions to use a drill bit. I then read on the forums to sync them anyway. I have a stock motor, but still had a lumpy off-idle low RPM feel. I made the tiniest adjustment to bring them into sync and that lumpiness went away. I have to admit, one side effect of doing that adjustment is that the "lope" or "cammed" sound at idle went away too. It went from sounding like a drag bike to sounding like a tame regular old street bike. Super smooth right at the crack of the throttle too.

I don't know how the drain works on the VM33, but a trick I learned a long time ago (that you and everyone here probably knows as well) is to put a piece of clear tubing on the drain nipple and run it up over the height of the top of the bowl. Then open the drain with the fuel on and you've got a sight glass to see the real level of the fuel inside the bowl. This is probably easier on the bench with an aux fuel supply than on the bike, especially if you have a vacuum operated petcock. It's a quick and easy test to do on a dirtbike.

Sounds like a fun bike!

[Rob S.]

I know the least of all the guys that have posted ideas here...

Not any more!

Yes I only run Shell 93 octane. And as far as pinging in 2nd gear at 5mph goes, I thing that is a different scenario than my problem as I am much much higher in the RPM range and it doesnt ping with me. I can step on it WOT and she will accelerate no ptoblem from 5th gear at 50mph without pinging. It immediately stops the "ratatatatatatata" as soon as I give her more throttle.

I would certainly do all that Ray suggests as I believe he is one of this site's most knowledgeable on the big GS engines, souped up or not. But, I was wondering if this is related to "lean surge". From the July 1982 Cycle World review of the new 1100e:

"Throttle response is good but there is a small amount of lean surge at steady-state cruising speeds and low throttle openings. It feels as though the carb pistons are undecided as to where, exactly, they want to position themselves. At higher road speeds, during hard riding, or in the fast-slow transitions of daily riding no carb problem is evident and the throttle is quick and responsive."

[bonanzadave]

"Throttle response is good but there is a small amount of lean surge at steady-state cruising speeds and low throttle openings. It feels as though the carb pistons are undecided as to where, exactly, they want to position themselves. At higher road speeds, during hard riding, or in the fast-slow transitions of daily riding no carb problem is evident and the throttle is quick and responsive."

Mine is bone stock and may suffer from this a little but it still pulls like a tractor with no hesitation. No down shifting required. 3rd gear from a dead stop only requires more throttle.

[londonboards]

[limeex2]

Your o2 sensor is only checking it with no load. If your willing to spring for a new set of carbs which it does not need.
1) check most logical suggestions list here
2) take it to a GOOD dyno man. It is the ONLY way it run as good as it will ever get. Seat of the pants, I hear this, runs poor because of oxy fuel. All guess work.
3) If you have that much time, effort and go fast goodies into a motor, show it a little love andgive it a some dyno time. You will be amazed at how it runs. Everyone of my bikes have been run on the dyno. On my Triumph Sprint my mileage went from 36mpg to 43mpg and runs absolutely flawless. This was on a totally stock bike My Gs1100 with every suggestion from people here, GSXR1100 carbs from a "GS carb guru" ran like sheet. Bring it to the dyno guru. Runs like a fuel injected bike. Flawless every throttle opening, slow speed (which is the hardest). I can roll the throttle from 1800rpm no funny noises, lurching. Better than new. Just my 2 cents worth.

[posplayr]

Your o2 sensor is only checking it with no load. If your willing to spring for a new set of carbs which it does not need.
1) check most logical suggestions list here
2) take it to a GOOD dyno man. It is the ONLY way it run as good as it will ever get. Seat of the pants, I hear this, runs poor because of oxy fuel. All guess work.
3) If you have that much time, effort and go fast goodies into a motor, show it a little love andgive it a some dyno time. You will be amazed at how it runs. Everyone of my bikes have been run on the dyno. On my Triumph Sprint my mileage went from 36mpg to 43mpg and runs absolutely flawless. This was on a totally stock bike My Gs1100 with every suggestion from people here, GSXR1100 carbs from a "GS carb guru" ran like sheet. Bring it to the dyno guru. Runs like a fuel injected bike. Flawless every throttle opening, slow speed (which is the hardest). I can roll the throttle from 1800rpm no funny noises, lurching. Better than new. Just my 2 cents worth.

This is probably very true. I think I got close only because I finally figured out that I needed to be able to measure AFR under a relatively constant load. I found a long hill within relatively short riding distance. There are not too many straight 6% grades that go for 1.5 miles with few Leos.

With a tuned 1100 accelerating on flat ground it goes so fast that your really can't tune anything even with a WB02. Plug chops are a joke. You need a quasi steady state condition where the floats and flow has stabilized to get a true AFR reading. On the dyno although it is an increasing speed it is accelerating slow enough to get a good reading on AFR without all of the dynamics.

And I did realize an surprisingly improved front wheel lift after getting the AFR better than what it has ever felt like before that.

[Rob S.]

...take it to a GOOD dyno man. It is the ONLY way it run as good as it will ever get. Seat of the pants, I hear this, runs poor because of oxy fuel. All guess work.
3) If you have that much time, effort and go fast goodies into a motor, show it a little love andgive it a some dyno time. You will be amazed at how it runs. Everyone of my bikes have been run on the dyno. On my Triumph Sprint my mileage went from 36mpg to 43mpg and runs absolutely flawless. This was on a totally stock bike My Gs1100 with every suggestion from people here, GSXR1100 carbs from a "GS carb guru" ran like sheet. Bring it to the dyno guru. Runs like a fuel injected bike. Flawless every throttle opening, slow speed (which is the hardest). I can roll the throttle from 1800rpm no funny noises, lurching. Better than new. Just my 2 cents worth.

And mine...

[jprice90]

Not trying to hijack, but I just need to chime in. I too have the "ratatata blahh blahh blah". More of a hesitation or stumble in the low range, 2000-1200 about from what I noticed with my 850. I was always thinking a sync, but I had a shop "do it", but to no change and it seemed it was running richer than when I had took it in.

Have you gotten this sorted yet?

[jprice90]

Are you using a vacuum petcock?
Be careful building that 82 crank.

I know this would make #3 real rich, now would it possibly make #4 also?
having an issue with 3 and 4, tuned the air mixture screws to lean it a bit just to see if the plug colors would change and nothing, 1 and half more turns in and they would've been bottomed out. Carbs rebuilt from Steve last summer

[Steve]

As far as vacuum syncing the carbs I bougt a Sudco tuning manual for them and they said specifically to not use vacuum gauges to sync the carbs as when you have the carb hats off it creates such a vacuum leak that your readings will be distorted. They said they recommended just syncing them with a drill bit under all the slides.

I know NOTHING about these carbs, but I get the impression that they operate somewhat similar to the stock VM carbs. Yes, I can see if the cap is off and the slide is loose, there might be a sizeable leak, but why can't you do your carb sync with the caps ON? Check the gauges, note what needs to change and how much. Take the caps off, note the new readings (which might be a bit different, make the adjustments that you noted previously. Put the caps back on, your sync might have improved. Yeah, it's a lot more work, but if it helps get the bike run better, it HAS to be worth it.

I know this would make #3 real rich, now would it possibly make #4 also?

This comment is in response to a question about a vacuum petcock. Just to make sure you know, but the petcock on your bike is connected to carb # TWO, not three. The carbs (and the cylinders, spark plugs, etc.) are numbered from LEFT to RIGHT, as you are sitting on the bike. #1 is under your clutch hand, #4 is under your throttle hand.

If your mixture screws are at 1.5 turns out, you might be running too lean at low throttle. Back when these bikes were new, they might have had that setting, but the carbs were set lean for EPA regulation, the carb has changed a bit over the years and the gasoline has changed a LOT over the years, all of which require a bit more opening on the pilot jets. Most of my bikes are in the 2.25-2.75 range and run quite nicely.

.

[mac1170]

I would also check that your pilot jet, has the crossdrilled holes, used on slide mikuni's, and not the cv carb style, which has only the jet diameter hole, could be leaning out, at low constant throttle, all the best.

[Paul.S]

Well it has been a while since I have posted here but I finally saved up the money and ordered a set of Mikuni RS36 flat slide carbs for it. I will let yall know if they fix the problem. As far as the guys who say I should dyno tune it, I have ran it on the dyno and it made 122whp but the a/f ratio was off alot. Since then I tuned it myself with the oxygen sensor under load going down the road and it made no difference. So hopefully these new carbs will do the trick!