I continue to be baffled by a rich-running condition in my 1980 GS1000G at low throttle settings. During the past two months I?ve carefully cleaned the carbs, replaced mixture screw O-rings with new, inspected mixture screws, replaced float valve and seat assemblies with new, checked float levels, replaced petcock with new, cleaned and flushed the fuel tank, replaced plug caps with new, checked coils, igniter box, and pulse generator.
Right now, my fuel mixture screw settings are:
#1 - 1/2 turn out from lightly seated
#2 - 3/4 "
#3 - 3/4 "
#4 - 7/8 "
I've got the main idle knob adjusted to get 1100 RPM at idle, hot with no choke.
Yesterday, on the advice of my friend and fellow GSR member Shaunt (ard) I removed the air filter from the airbox, replaced the airbox cover and went for a ride for half an hour. The bike ran just the same without a filter, as with the filter, which is to say it ran fine at commuter speeds and at engine RPMs generally around 3000 to 4000 RPM with occasional idling at red lights, etc. The plugs lightened up just slightly without the filter. I had been of the understanding that GS bikes run like total crap without an air filter, and particularly run like crap without a filter at RPMs above approximately 3000 RPM.
So, my question is:
What are all the possible causes of a rich-running condition, particularly when the bike runs rich at low throttle settings around town, but runs fine at all throttle settings and the plugs lighten up just fine after 10-minutes or so at highway speeds?
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