Idling/Rev/Carb Problems With GS1100 and GS750

[Guest]

I can not take it any longer! Heres my situation . . .

I own two bikes, a 78' GS750 (which I'm suspicious is older than a 78, it only has one front disc brake) and an 82' GS1100L shaft drive.

Both of my bikes have an issue with them, they suck at any kind of consistent idling. I'll use the 1100 as an example. When I start it up if I'm not giving it gas it will stall, its normal, I get that, the engine is cold. But my problem is even when its warmed up and I've been riding for half an hour, when I'm at an intersection the idle will be so low that it will putter out and stall if I don't keep giving it shots of gas. But then, when I do that, or sometimes when I've just come to a stop at an intersection, the idle will suddenly climb to like 2500 even though I haven't touched the gas! Both bikes do this. Its very frustrating, popping it into gear at that high of a rev is difficult sometimes and it jolts. So when I'm in this situation, I always end up popping it into gear and slowly letting go of the clutch to bring down the rev. I usually have to keep repeating this, and then sometimes the rev will be low again to the point where I have to give it gas again.

I've taken apart the carbs on the 750 before and greased my throttle shaft and replaced the throttle cable.
The 1100 throttle cable seems fine, it shoots back better than the 750 does.
Thats another thing, I have a brand new throttle cable on the 750 but the throttle still doesn't shoot back very good, I can be riding it and let go of the throttle and it hardly lets of the throttle.

I'm at a point where I want to rebuild the carbs on both bikes, but I'm not sure thats even the problem. I was thinking maybe they aren't sealing well or something. Also I was wondering if the air filter would affect revving. I put in a brand new filter in the 750 last summer, I haven't even looked at the one in the 1100 though.

PS, I know how to adjust the idle speed, I do it often, but when I have the revs higher at idle, when it does its rev jump its about at 3 which is so hard to get in gear sometimes.

Everyone tells me theres tons of info for all this on the internet, but I can never find anything to help me. I've got more questions yet as well, but I'll start here. If anyone can give me any sort of advice I would greatly appreciate it.

[mrbill5491]

Check the routing of your throttle cable on the 750, sounds like it maybe binding somewhere. Check all your rubber boots (seals) on the carbs, if they aren't sealing, then they can suck in air and cause a lean condition causing the idle problems. I'm assuming you have the stock air system on both bikes. they need to be all air tight.

When were the carbs last serviced? If cleaned at one time how were they cleaned?

When is the last time you had the valves adjusted?

[JJ]

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

Read and absorb... then DO

[tkent02]

'78 and '79 750s came with one or two brakes. Maybe '77 too, or a lot of people converted them…

[Rob S.]

I'll use the 1100 as an example. When I start it up if I'm not giving it gas it will stall, its normal, I get that, the engine is cold.

That's not normal, at least not for the 16-valve.

Normal is to rev to 4k or so until the choke is backed off.

[hjfisk]

Check your intake boots, and o-rings , you have a vacuum leak somewhere , and when were the carbs properly dipped and cleaned last. Also you need to replace the o-rings, Robert Barr here on the site sells O-ring kits very reasonable.

[tom203]

Yes, air leak. Pull the carbs on the gs1100 and clean them properly and replace o-rings. Do some reading and don't take shortcuts

http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

There is no need to put up with random idle issues- these bikes should idle nicely/consistently after a brief warmup.