Author Topic: 2002 gs500 weird idling problem. need help  (Read 670 times)

Offline gsgibbas

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2002 gs500 weird idling problem. need help
« on: August 22, 2019, 06:46:35 PM »
recently bought a 2002 gs500 as a first bike and has been a little project for some time.
after cleaning the carbs and tank, i was able to get the bike started enough to ride it around but it all felt very off. come to find out, the poor thing was only running on one cylinder. i managed to fix that after new plugs and cleaning the plug wires. here's where it gets weird;
it starts great with choke and idles like it needs the carbs synced (which is my next job with it). once the bike is warm, it rides and revs well enough to have a great time on the road. when coming to a stop and the revs are above 2k rpms when i pull the clutch in, the revs climb to over 3.5k. if i leave the engine to slow to below 2k before pulling in the clutch, it idles fine at 1.5k. if i apply any throttle while it idles at the 1.5k, it begins the climb again, only not to return until i manually slow it down or ride.

what could be the problem here? the air/fuel screw is set to 3 turns out on each carb and the throttle stop is at a setting were it has the ability to idle at the 1500 rpms.

i apologize for the ignorance as this is all very new to me.

thanks!
« Last Edit: August 22, 2019, 06:48:16 PM by gsgibbas »

Offline mr72

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Re: 2002 gs500 weird idling problem. need help
« Reply #1 on: August 22, 2019, 08:18:45 PM »
Your idle is set way too high, that's the main problem. And it may be too rich. Three turns out of the pilot needle adjuster is basically the upper limit. Did you put bigger jets in? Did you replace o-rings? Reset floats?

But just to get it working correctly, reduce the "idle speed" screw so the throttle can be fully closed at idle, then start with choke and go ride. Ride some more, and more, and more, reducing choke for the first few miles. Take it all the way off choke after about 10 minutes riding, then after about 20 minutes riding it should be fully warmed up and you can now set the idle speed to about 1100 rpm on the bike tach, if it is not already running that way. That should clear up your hanging idle problem. But it might reveal other problems.

If you have't yet, you might consider doing this:
https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html

Note that I am talking in the blog post about the earlier carbs so some things don't apply directly (example, you want size 20 pilot jets for the '02 carbs). But in principle it probably all works.

Offline The Buddha

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Re: 2002 gs500 weird idling problem. need help
« Reply #2 on: August 22, 2019, 08:50:15 PM »
recently bought a 2002 gs500 as a first bike and has been a little project for some time.
after cleaning the carbs and tank, i was able to get the bike started enough to ride it around but it all felt very off. come to find out, the poor thing was only running on one cylinder. i managed to fix that after new plugs and cleaning the plug wires. here's where it gets weird;

Not weird at all - stock bikes with US spec jetting do this all the time.
 
it starts great with choke and idles like it needs the carbs synced (which is my next job with it). once the bike is warm, it rides and revs well enough to have a great time on the road. when coming to a stop and the revs are above 2k rpms when i pull the clutch in, the revs climb to over 3.5k. if i leave the engine to slow to below 2k before pulling in the clutch, it idles fine at 1.5k. if i apply any throttle while it idles at the 1.5k, it begins the climb again, only not to return until i manually slow it down or ride.

This is a sign that its lean at idle. Or sucking air (intake manifold leak). Check with wd40 and if no leak, richen the mix at idle with air screw. Also synch ot before fooling with air screw just to be sure. And valves are in spec ??? Make sure of that too before synch, valves hanging open affect synch too. Loose valves don't affect it, so if you can hear each valve clack nicely, then synch and valve adjustment can be independent of each other. But don't synch with tight valves.


what could be the problem here? the air/fuel screw is set to 3 turns out on each carb and the throttle stop is at a setting were it has the ability to idle at the 1500 rpms.

i apologize for the ignorance as this is all very new to me.

thanks!

Air screw set to 3 is where I start out a 20/132.5/1 washer setup - and remember that is 1 size richer all across than stock, so if you really want to fix it right, jet it to 20/132.5/1/3 - else atleast open the air screws 1/2 - 1 turn. You don't run much risk of it falling out before getting over 6 or so, but 3.5 to 4 should do it with your rather mild lean problem at idle.

Cool.
Buddha.
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Offline gsgibbas

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Re: 2002 gs500 weird idling problem. need help
« Reply #3 on: August 22, 2019, 10:42:17 PM »

This is a sign that its lean at idle. Or sucking air (intake manifold leak). Check with wd40 and if no leak, richen the mix at idle with air screw.

So, just to clarify, turning the screw to the left and backing it out further will enriched the system?
It has stock everything as far as I know. And I havenít checked the valves yet, have to get feelers first.