Well I dug the carbs out of the 91 GS500 because of the tremendous fuel leak from the overflow tube (see my previous post).
Several of you thought it was stuck floats but when I opened up the bottom the floats appeared to be in good working order. One of the main jets a had a little bit of crud in it but for the most part I thought it looked pretty good. I did notice that a one of the little "O" rings on was deformed. This particular "O" ring is when you take of the top of the carb cover.
It is possible that the float(s) were stuck and by removing the carbs and bumping them around on the workbench them freed them?
Everything on the carbs is so contingent on vaccuum so I'm going to replace all the O rings and gaskets and put it back together and see what happens.
I have to admit that because the majority of bikes in my stable are BMW's and EFI's I'm not as savvy on carbs as I would like to be so any opinions posted now would be appreciated before I get everything back together.
Carb cover? Are you referring to the float bowl gasket or the vacuum cap O-ring?
It is still likely that one or both of the floats were stuck. What generally happens is varnish on the float needle and the needle guide hardens when the carbs are drained for an extended period. Check the needles in both carbs carefully to see that they move freely and are free of foreign matter. It is possible that the piece of dirt you found in the carb was lodged in the needle guide or under the needle itself.
Since you found a piece of dirt in the carb I suggest you undertake a thorough cleaning of the float chamber, and all the fuel passages. Use a can of carburetor cleaner for this purpose. Replace your in-line fuel filter, or install one if you don't have one. I prefer sintered Bronze filters because they are field-maintainable. Something along these lines works well: http://www.russellperformance.com/tech_center/motorcycle_fuel_filters.htm
I agree completly with your plan to replace all the O-rings and gaskets. Inspect your vacuum diaphragms carefully for leaks. Also note your jet sizes for future reference.
Have fun! Carbs are a pleasure to work on once you understand them. :)
It's possible. You have to jiggle and wiggle it quite a bit before it's free of the engine and all the cables.
I highly recommend a complete rubber replacement. When I took apart my carb (and broke the piston guide if you were reading the thread) all I did was clean the emulsion tube, soaked the carbs in cleaner (be sure all plastic and rubber is out of the carb before you do this), and I changed out all of my o-rings. It runs soooo much better than it did before. Nice and smooth through the entire RPM range (I actually got it over 10k). Oh, and I adjusted the valves, which you might want to go ahead and check since you have it torn down. It's just 10 bolts.
Don't worry about your familiarity with carbs. These are very simple. I didn't have a clue when I began, and I can now completely disassemble one blindfolded, and I've owned this bike for lless than 2 months.
Carbs are fun when you completely understand them and if you have the time to work with them. EFI is a lot more convienant, but offer's less control. Analogy would probably be an automatic transmission versus manual. Sure Manual is fun, but ever get stuck in traffic with a manual during a commute? Not so fun huh?
Heed that advice (http://gstwins.com/gsboard/index.php?topic=25045.msg258221#msg258221). With the carbs overflowing in all three positions of the petcock there's definitely something fishy with the chicken.