Do GS1100s naturally run rough at low speed?

[Paul.S]

My 1982 GS1100E runs rough at about 40-55 mph when just barely on the throttle cruising through town. Instead of the engine going "vrooooooooooooooom" it goes "Ratatatatatatatatata" or atleast that is the best I can type it lol. The bike has done this since I bought it. I totally rebuilt the engine and pretty much restored the bike and it still does it. It has brand new Dyna 2000 ignition timed to 35 degrees, Mikuni VM33 smoothbores with pods, V&H street/strip camshafts, ported head with I beleive +1mm intake valves, I degreed cams to 106 intake 108 exhaust, it has 1198 kit with 10.5/1 compression ratio, and a Kerker exhaust system. I put a digital wideband 02 sensor in the exhaust and tuned the carbs almost perfect but still no change. Degreeing the cams did not help. The new Dyna ignition changed nothing. Compression is even throughout all 4 cylinders. New plugs changed nothing. New spark plug wires changed nothing. I am beginning to think that is just how these motors run? Anybody have this same problem? The bike runs perfect other than that.

 

[jsandidge]

Try a lower gear.

 

[Paul.S]

Even if I downshift a gear it still does it. It is about 2800-3500 rpm where it happens most. Do you think the street-strip cams could cause it? They are .345" lift and 258 degree duration.

 

[posplayr]

running a little lean when lugging and it is pinging. Step down a gear and then give a twist.

 

[GregT]

Big carbs, cams, compression...no it won't want to run like a stocker at low revs.

Vacuum sync can often help on VM33's - a lot of people using them simply physically sync the slides but sometimes that's not close enough.

 

[posplayr]

I have close to the same thing except it is 1166 and 340 cams degreed about the same and if I'm in 2nd gear at 5 miles an hour and I put on the throttle I get that Tatarstan sound which is pinging.

 

[posplayr]

Who knows how much you shaved the head you absolutely need to run premium

 

[Paul.S]

running a little lean when lugging and it is pinging. Step down a gear and then give a twist.

Thats what I thought too until I put the 02 sensor in it and realized it is actually running on the rich side when it does it (not very rich). 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 did notice today when I pulled the plugs that the #2 plug is darker than the rest as if it is getting more fuel than the others. I have the same size jets of course in all the carbs so maybe there is something wrong with the vm33s? Maybe I should try a new set of Mikuni RS36 carbs? But that would be an expensive test!

 

[Paul.S]

Who knows how much you shaved the head you absolutely need to run premium

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.

 

[posplayr]

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 guess my bike runs a little rich at idle as well. It was tuned using a LM-2 WB02 as well.


Well the only other thing that make that kind of nice is the clutch. Did you do a HD clutch? How do the grooves look inside of the clutch? Using the thin clutch disks; they beat the hell out of the basket.
You said this was a 1982 so I assume you did something with the crank although that would not cause the noise you mention.

 

[Paul.S]

I guess my bike runs a little rich at idle as well. It was tuned using a LM-2 WB02 as well.


Well the only other thing that make that kind of nice is the clutch. Did you do a HD clutch? How do the grooves look inside of the clutch? Using the thin clutch disks; they beat the hell out of the basket.
You said this was a 1982 so I assume you did something with the crank although that would not cause the noise you mention.

It does have a V&H "super hub" clutch basket that is welded to the big gear. It is worn out and needs to be replaced as it does have grooves. The clutch pack I am unsure of and the previous owner claimed it had stock springs but IDK the clutch is pretty hard to pull. But, I am almost sure the clutch is not the cause as the engine itself makes the sound its not like a rattling sound or anything of that sort. And when it is making the ratatata sound it will stumble just a bit if you try taking off hard while it is doing it.

 

[posplayr]

It does have a V&H "super hub" clutch basket that is welded to the big gear. It is worn out and needs to be replaced as it does have grooves. The clutch pack I am unsure of and the previous owner claimed it had stock springs but IDK the clutch is pretty hard to pull. But, I am almost sure the clutch is not the cause as the engine itself makes the sound its not like a rattling sound or anything of that sort. And when it is making the ratatata sound it will stumble just a bit if you try taking off hard while it is doing it.

Well to answer your original question, no it is not normal. I have ridden my bike many miles on rallies and there are no unusual characteristics in the running. My understanding is you can go to the 0.348" cams and they are almost as tame and there are not any distracting behaviour. Realize the GSXR cams have similar lift stock.

There are even several discussion that have taken place about the quality of ride of the BS v.s BST v.s RS carbs and none of them have such problem as you describe. If you clutch is worn out then I would look there. I don't think it has anything to do with cams,piston,carbs, ignition, or any of your other hop up mods.

 

[rapidray]

2 things, FIRST: take 2 degrees out of the timing. On the street, with the inconsistencies of pump gas, it is too risky to run more than 33 degrees of timing. I only run 34 in my dragbikes, with race gas. SECOND: if you have not done it yet, VACUUM CYNC the carbs!!!! I can NOT stress this enough!!! It is a WORLD of difference!!! Set the idle at 2500 to sync them & turn the idle back to normal once completed. It will make a HUGE difference in the way the bike runs if they are off!
Ray.

 

[Paul.S]

I will have to do that Ray. I just noticed raw fuel residue leaking out of my #2 cylinder exhaust port so something is wrong with that #2 carb for sure. What could cause one carb to dump that much more fuel than the others? They all have the same jets and are just mechanically synced. Could being out of syn cause an overly rich condition like that? I would think it would have to be pretty darn rich to leak fuel residue out.

 

[Guest]

I will have to do that Ray. I just noticed raw fuel residue leaking out of my #2 cylinder exhaust port so something is wrong with that #2 carb for sure. What could cause one carb to dump that much more fuel than the others? They all have the same jets and are just mechanically synced. Could being out of syn cause an overly rich condition like that? I would think it would have to be pretty darn rich to leak fuel residue out.

Check the seal in the choke circuit in #2 carb they are prone to leaking and can cause one cylinder to run rich.

 

[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!

 

[Guest]

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."