engine idle creeps up

[79GS850VETTER]

I have a 79 GS 850. I have been trying to figure out what is going on with my carbs. At idle and only when the engine is good and warm the idle RPM creeps up. The problem seems worse if it is cold out or if I am at higher altitudes. I had the carbs cleaned and new main jets installed last fall. I put in an electronic ignition as well but the problem persists. Idle jets were back ordered last year. The shop says they are available now so they are on order but they have not arrived yet. I am hoping that fixes the problem. Any other suggestions that I should be looking at?

 

[hampshirehog]

Classic air leak symptoms. I suggest having a look at the carb manifold O rings, the carb manifolds and the airbox to carb rubbers. Or maybe your airscrews are set very weak.

BTW, if you've had to wait since last year for the shop to get in your pilot jets I suggest you change shops. Even in the UK I could have them here in under a week.

 

[twr1776]

Today, 02:32 PM hampshirehog Classic air leak symptoms. I suggest having a look at the carb manifold O rings, the carb manifolds and the airbox to carb rubbers. Or maybe your airscrews are set very weak.

+1, what do your plugs look like? Have the intake boots, o-rings, and airbox to carb rubbers been replaced? If they are originals they are most likely bad and causing your creeping idle.

Cliff will be along shortly for your official greeting but here is a link to his website. The top 10 issues noted and BWringers 15 step program are really mandatory to any GS so you can have a reliable bike.

http://members.dslextreme.com/users/bikecliff/images/GSR_Greeting.html

 

[79GS850VETTER]

Thanks. Intake boots are new. Air box has been cleaned and all looks good there. Plugs look nice. The last trip I made I fiddled with the airs screws but the idle creep seems inconsistant and I could not find a setting that solved it. I sprayed brake cleaner around the intakes as well to see if that showed a leak but it didn't change the RPM.

By the way....great site, I wish I had found this a long time ago.

 

[tkent02]

Replacing jets won't do anything unless they are a different size, you don't really know what size you need. What method have you used to set the fuel screws underneath the carburetors?
They work together with the air screws to control idle mixture.

How does it run other than the creeping idle?

And, clarify if you will, do you mean it idles at a slightly higher RPM when the engine is hot, or do you mean the idle speed comes up quickly, like it rises up higher and higher as you sit at a light or something? Something like going from 1,000 to 1,500 to 2,000 and on up within a short period, like 20 seconds or so?

 

[79GS850VETTER]

When I replaced the main jets the numbers were almost worn off and the bike ran better with the new ones. That is why I was hopeful about the idle jets, I think they may be worn larger than they should be.

The creep happens at idle, like at a stop light. The idle slowly climbs to about 2500 rpm. If I work the engine slightly be releasing the cluch part way for a moment, it will drop the idle back down and the process will start over and slowly creep up.

In saying that though sometimes when I come to a stop the idle is already up. If I blip the throttle it only makes it higher so I don't think the needles are sticking.

The shop I was at is thinking it may be worn sliders in the carbs. I'm not sure about that diagnosis.

The engine runs fantastic other than that. At highway speeds my rpm guage bounces around a bit +/- 500 rpm and it has crossed my mind that whatever is causing that may be related. The rpm bounce is not consitant either and may just be the head or cable.

I had the carbs synced last fall and they set my idle screws to 1 1/2 or 2 turns out. I cant remember which one but I could check on the bike if you want.

I am suspicous that I am running rich at idle. Since it seems worse at altidude and in the cold which both richen fuel mixtures. It just seems odd to me that it is not more consistant. I've had 2 strokes that are finicky about fuel mixture but I did not think a 4 stroke would show significant differences with a 15 degree change.

 

[cdnoel]

Bearing grease.

Bearing grease.

Try a little smear of hi-temp bearing grease on the O-rings. Never hurts on the carb connections as well. Dry O-rings always give me fits so I always give em a little smear.

 

[tkent02]

I am suspicous that I am running rich at idle. Since it seems worse at altidude and in the cold which both richen fuel mixtures.

Higher elevation will make it richer, lower temperature will make it leaner, all else being the same. Higher elevation or temperature makes the air less dense, lower elevation or temp makes it more dense.

 

[terrylee]

My son has the same bike and the same problem. Still dealing with it, but have made improvement. Seal airbox with weatherstripping (should be thread on here about that), and turned the fuel mixture screw more lean and then adjusted air mixture screw by ear for now. It is also possible that a needle vavle under the floats may be sticking at times. I'm planning on replacing my son's. Just my thoughts hope it helps. terrylee

 

[robertbarr]

Intake leak or carb sync, or some combination of the two. Have a look at both.

Your bike is a '79. Replace the intake O-rings as a matter of sanity maintenance, or the symptoms will drive you nuts.

 

[teddux]

Could be your choke assy. - leaky (worn plunger/damaged rubber seal, bottom).

 

[79GS850VETTER]

I know the airbox outer side rubber seals are not in great shape. I did not realize that they needed to be air tight. I'll try that first since it is the easiest. When you say weatherstripping are you talking about the 1" wide foam stuff with an adhesive tape on one side? If so how do you cover the whole area that that rubber seal covers? If my memory serves me it is about 2"x3".

 

[Ponderosa]

?

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Whe the RPM climbs like that have you tried to turn it down with idle adjustment? Does it respond? Check throttle cable for any kinking, it does sound like a vacum leak, but cover all the bases...

 

[79GS850VETTER]

Yes, idle adjustments change it but then it won't idle when I first come to a stop before it has a chance to start climbing. I don't think it is the throttle because it is not consistant and if I blip the throttle it only makes it rev higher. The throttle seems to operate smooth. vacuum leak might be a possiblility but spraying brake clean around the engine should show an indication of a vacume leak but I get no change when I do that.

 

[tkent02]

I know the airbox outer side rubber seals are not in great shape. I did not realize that they needed to be air tight. I'll try that first since it is the easiest. When you say weatherstripping are you talking about the 1" wide foam stuff with an adhesive tape on one side? If so how do you cover the whole area that that rubber seal covers? If my memory serves me it is about 2"x3".

Your airbox has the metal covers over the ends, doesn't it?
These covers need to be sealed around the perimeter, and across that divider across the center, as above the divider is filtered air, below it is unfiltered. Even small leaks here will make the engine run lean, especially at idle.
The climbing idle is exactly what is likely to happen from a poorly sealed box. Single stick foam tape and a pair of scissors and you are good.

 

[79GS850VETTER]

I was all excited that it could be such an easy fix....but...no such luck. I put the heavy dark foam weather stripping on and my problem persists. I took it for a run today. At start up and a short warm up the idle is great. After about 5-10 minutes of highway riding the idle was up around 2500. A blib of the throttle brought it down to normal for an instant then it creeps back up to 2500. If I wait about a minute it will come down to 2000.

I adjusted the idle at that point to 1500 and it runs ok but it will not idle at all when the engine is cold to warm. After that it idles at about 1500 but if left idling for a while it will drop to 1000.

Its workable but I know this is not how the bike use to run so I know something is not right.

 

[Nessism]

Did you change the intake boot O-rings lately? If not, that is a highly likely source of the problem. If that's not it you might want to tweak the fuel and or air screws to richen up the mixture at idle. Where are the screws set now?

 

[81gs1100]

All great things to check out, however I didn't read if anyone had mentioned the petcock leaking gas or air into the signal tube to the #2 cylinder. A bad petcock can leak fuel down the tube, or air which will mess with your idle. Pull your plugs after letting it idle high for a few minutes. See if #2 is running leaner or richer then the other cylinders.

Also when was the last time the valves were adjusted? If the problem only happens when the motor is warm/hot, maybe the valves are a bit tight affecting the ablility to accept and keep a proper air:fuel ratio charge in the cylinders.

 

[rideOn]

my rpms varied until i replaced the intake o-rings and re-worked the carbs. now she's good.

 

[Matchless]

Intake leak or carb sync, or some combination of the two. Have a look at both.

Your bike is a '79. Replace the intake O-rings as a matter of sanity maintenance, or the symptoms will drive you nuts.

As Robert says if everything is physically correct and you have not resychronised the carbs after taking them apart......