What to do about idle?

[TheDooman92]

My bike is idling around one thousand RPM when warm, sometimes it will still die after half an hour ride as the idle does not seem to change while warming. After a good warm-up and adjusting the idle adjuster and bringing the bike up to 1200 RPM at idle, leaves me with a hanging idle issue. How can I get the optimal idle without the hanging idle problem? Does this have anything to do with idle mixture? Thanks kindly!

Andrew.

[mr72]

1000 rpm is the optimal idle speed for your bike. Nothing wrong with that. The tach on the bike is not accurate anyway.

[TheDooman92]

Hey Mr72. Are you certain that optimal idle speed will allow the bike to die after warming up? This is normal? I have to give the bike a little bit of throttle just to keep it running at stops. I am using original spark plugs from 2009, would it help to change those out?

Thanks kindly,
Andrew

[mr72]

It may be too lean on idle, which might be why it's stalling. But a correctly tuned GS500 should happily idle at 1000 rpm.

Read my blog post on the topic. It walks through this in detail.

https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html

[cbrfxr67]

Was about to link that into the thread.  I didn't know you wrote that.  Good stuff there!

I printed that and more for uhm bathroom study time every evening

[TheDooman92]

Do you think fresh spark plugs may also help with keeping the bike running at idle? Would you also suggest using the choke at stops as suggested in the post you linked to me?

[mr72]

Changing the spark plugs won't hurt. It's unlikely they are related to your problem. The bike does produce less voltage at low rpms so the spark can be weaker, and this is a function of the regulator/rectifier and stator. But there is also much less fuel to ignite so a weaker spark at idle should be totally fine. But for under $10 and so quick to change, I see no reason not to change the plugs. Just don't expect a difference in idle performance.

If your bike really and truly stalls when idling hot at 1000 rpm then I would do a compression test next. Pending the result of that, suspect tight valves could be causing poor compression which would lead to bad idle, or if not that then other issues like valve seat wear or rings. Low compression will definitely cause it to not idle correctly.

I suspect others on the forum will potentially advise that vacuum leaks can cause poor idle as well, which is likely true but the fix is to replace all of the o-rings and get the carbs sorted to eliminate the possibility of vacuum leaks. While you're at it you wind up fixing the mixture and other issues as well. All one big fix. $40 in parts, a half a Saturday of quality time with your bike, and you'll be golden.

[qcbaker]

I suspect others on the forum will potentially advise that vacuum leaks can cause poor idle as well, which is likely true but the fix is to replace all of the o-rings and get the carbs sorted to eliminate the possibility of vacuum leaks. While you're at it you wind up fixing the mixture and other issues as well. All one big fix. $40 in parts, a half a Saturday of quality time with your bike, and you'll be golden.

I was gonna mention the possibility of a vacuum leak, and this is basically the same advice I was going to give.

[TheDooman92]

Thanks for getting back to me guys, one last question: could the possibility of one of the vacuum hoses being hooked up incorrectly (reinstalled in the wrong place) result in an issue like this (poor idle)? Even though the bike runs fine otherwise? I have a feeling that when I first changed some gaskets on the carbs that something was put back wrong, and have always wondered about whether I hooked the vacuum lines up in the right spots (I kind of winged it). Thanks guys,

Andrew.

[qcbaker]

This should help:

[herennow]

Is that not the picture with Fuel and Res swapped, can't remember but I'm sure my hoses cross, not nice and aligned like these. ?

[qcbaker]

Is that not the picture with Fuel and Res swapped, can't remember but I'm sure my hoses cross, not nice and aligned like these. ?

I believe it is. but the vacuum hose routing should be correct.

[TheDooman92]

I was just asking, if the hose routing is off, can this affect idle?

[qcbaker]

I was just asking, if the hose routing is off, can this affect idle?

Honestly I'm not 100% sure but I doubt it? I posted the routing diagram so you could ensure it was correct, not because I believe it to be the source of your problem. I'm not an expert, and someone (mr72, probably lol) can correct me if I'm wrong, but my understanding is that the vacuum hose is what allows fuel to flow through the petcock while in the ON and RES positions (its vacuum actuated). If the vacuum hose is not routed properly, fuel would not flow and the carb bowls wouldn't fill so the bike wouldn't run at all unless the petcock is in the PRI position (which is gravity fed, not vacuum actuated).

I think your issue is most likely related to a vacuum leak in the carbs. Improperly seated diaphragm, leaking gasket or o-ring, something like that. Could also be jetting, but I think thats less likely unless you replaced one or more of the jets.

[mr72]

I don't know what year your GS is but I am pretty sure there's no way to get the vacuum hose routing wrong since there is only one, at least on a Mk1. I mean, I guess it's possible you could just leave that vac port wide open where it is supposed to connect and instead connect it to one of the diaphragm cover vacuum ports and it would screw stuff up but that's not really a hose routing problem, that's a just didn't assemble it right problem.

If you have a vacuum LEAK it could cause idle issues. That's why you go through the carbs and fix stuff. That vacuum hose going to the petcock could be leaking, which would be like any other vacuum leak, plus would make the carb be starved for fuel at high revs or big throttle opening.