recently bought 90 gs500 pretty good shape, but idle is very irregular and will rev very high without me even on the bike.  also getting bad back firing when off the throttle.  looking for help. :dunno:

sounds like gummed up carbs to me -- pull em off and give em a good cleaning, can't hurt either way

Welcome!

I'll second the carb cleaning. Also, check the airfilter; make sure it's clean. And, check that the spark plugs are tight.

will i need to get a carb kit if i take it apart to clean.  i have the clymer manual but am new to cycling.

Shouldn't, but your bike is a '90 (15 years old), you could drop a floatbowl and inspect the rubber inside and go from there, or just be safe and order the set anyway. I really think you wont have to.

Hey, I'm having the same problem on my '96 E. I've only had it for a month, and I know that the previous owner drilled some holes in the stock exhaust but didn't re-jet. Also, I pulled off my spark plugs and noticed that one was normal, and the other was black as night... any ideas?

Cheers

rrbma, do you turn the choke off (away from you) once the bike is warm?  It only takes a minute or less...

I would 3rd the carb cleaning. Just go to local auto store and get some "d12" carb cleaner (I think that is what it is called) and a couple bags of mixed small o-rings.

you may have some worn out o-rings with a bike that old. My bike is a 2000 and when I cleaned mine I found that the o-rings that help hold the floats in were rotten...

Also see:
http://gstwin.com/carb_work.htm

And, this: http://gstwins.com/forum/viewtopic.php?t=18966

I had a similar problem and was able to fix it by adjusting the timing.

rebuilt and cleaned well runns better but in each kit ended up with one very small o-ring unused didn't want to take to much apart but i folloed clymer's to a tee. :dunno:

Quote from: Chris.t.CollinsI had a similar problem and was able to fix it by adjusting the timing.

so how exactualy did you adjust the timing???

Quote from: rrbmabut in each kit ended up with one very small o-ring unused didn't want to take to much apart but i folloed clymer's to a tee.

Probably the ones that go in under the tops of the carbs.