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Unstable idle

  • Thread starter Thread starter Scratcher09
  • Start date Start date
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Scratcher09

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Background:

This is an '82 GS1100G. I recently cleaned and lined the tank. I thoroughly cleaned carbs in an ultrasonic cleaner and replaced all o rings. Also checked valves and all were within spec. Stock air box with new filter and stock exhaust. Petcock seems to working as it should. After servicing carbs it fired right up and I synched carbs. The idle would slightly wonder sometimes. Occasionally it would seem to be idling too low and I would adjust accordingly and it would be fine and then three rides down the line it would idle too high and I would adjust again.

Now it's getting worse. Last night it was low so I adjusted it almost a full turn. When adjusting it, almost a full turn was having no affect and then all of a sudden it bumps up to 3k rpm. I know to only adjust a bit at a time and pull the throttle a few times to let it settle in between adjustments. But I am wanting to know what can be causing this erratic idle. Any input would be appreciated.
 
Check your ignition. Look at the plugs and the caps. Old plugs and caps won't fire as well and will cause idle issues. I chased vacuum leaks and fuel problems for months on my 81 kz1000, and once i had them fixed i still has throttle and idle issues. It turned out to be my coils were shot. I would also check your carb manifolds for vacuum leaks and sealing to the head. For the plugs, you are checking for the condition and color. Good plugs should be a tan-ish color, lean will be white, rich will be black. Plugs would be the first thing to look as since they are probably the easiest thing to get to. That will tell you where you need to look where your problems are.
 
Intake manifolds are new. Plugs look a bit darker than tan but not sooty. How would I know if coils are bad?
 
The coils should produce strong blue spark. Anything lighter in color and the plugs or plug caps can be bad and need replacing. Bassclif has a database of all gs factory service manuals, and the test/check procedures are in there. There's a chance your coils are going bad. I would also do the signal generator test and ignitor test as well if your coils and plug caps test good
 
Also, have you bench and vacuum sync'd your carbs. I may be pointing you in the wrong direction if you haven't done either of the syncs
 
I have bench and vac synced carbs. Also, I recently noticed that the head gasket is slightly leaking on cylinder one. Could this have any affect on the idle?
 
How far open are the pilot screws? If they are open less than 3.5 turns you may want to try that. Are the airbox boots sealing to the backside of the carbs? They need to be, without any path for false air to enter. Are the airbox side covers sealing to the airbox? You may have to replace the foam if it's deteriorated.
 
New intake manifold orings?????? If not, thats also a source for vac leaks Mixture screw tips all nice and pointy...nothing broke off down the hole???
 
I replaced the foam in the air box and the boots seem to be ok. The o rings were replaced when I installed new intake manifolds. Anyone know if the leaking head gasket could be the cause?
 
Clamps do stretch also. Even though you tighten them as much as they can go, they wont squeeze the rubber tightly around the carb throats. Just another thing to consider.
 
.............. and is the clutch cable routed correctly. It can interfere with the throttle.
 
Good one on the cable..I got a bike once and everytime you went left it surged from the pull on the cable being wrapped around the steering stem wrong.
 
Yet another thing i didn't think of. Is the throttle cable properly adjusted? If not, your throttle will jump with the bars turned to the left if it's too tight
 
I know this thread is a few months old. But I am having a similar issue with a wandering idle. Did the OP ever figure out the issue?
 
Did you replace the manifold boots at all? Mine are rough looking, but I sprayed carb spray and tried using propane to check for leaks and didn't get any definitive results. So I am thinking about just replacing them, but I cringe at spending $130 and not getting actual results.
 
Probably easier if you start new thread on your bike's (81 gs850 ?) issues to save folks from diving into old threads. Sounds like you have erratic/hanging idle, but your old thread mentions rich condition.
 
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