bike will not idle under 4000 and backfires. I just bought the bike for cheap. it has around 43000 miles, I know that is very high but I like the bike. I have cleaned the carbs twice and replaced the diaphragms on top. while idling at 4000 I can see the jumping spectacle in the carbs. also I have replaced the plugs, fuel lines and head cover gasket. not sure what could be causing the issue. any help would be great.

Could it be a jet issue?

Is it dying from fuel starvation at the low RPM?

not real sure. I am a mechanic but don't work on bikes much. how would I go about finding out if it is

Deff a carb issue. does it have stock exhaust and airbox or is it aftermarket? if its aftermarket, were the carbs jetted? you can tell by the cap that has been drilled on the bottom of each carb. Ill post a picture if I can find a decent one.

On the bottom.. idle air mixture screw. Usually has a cap unless you drill it out to adjust for aftermarket exhaust or intake

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bike is full stock and trying to keep it that way. could bad valves cause this sort of issue. I also forgot to mention that it only runs at half or full choke.
how many turns out should the mix screws be

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

Ben2go posted this link. It seems to be an easy read

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It's deff the carbs. You need to find the manual and see factory setting for the idle mixture screw if it's drilled. Choking it means it's running lean and and needs adjusted.. I unless I have that backward

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http://www.gstwin.com/rejet.htm

very good read!

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THANKS TO EVERYONES POSTS. GONNA TRY RESETING THE MIXURE SCREWS. WILL REPLY IF IT WORKS. THANKS AGAIN

A thorough going through of the carbs is never a bad thing,

but your symptoms sound far more like what was wrong with mine: totally neglected valves.

Make sure that the valves clearances are in spec (the GS can display a tendency toward tight exhaust valves; a not altogether uncommon practice here is to set them wider for extended service intervals).

The cure for my coughy, sputtery bike: new intake manifolds, carb jets cleaned, valves adjusted -> purred like new kittens.

Personally, I'd make sure the valves are tidy before messing around with mixture screws.

+1 for cWJ comment. Don't mess with cars and they don't mess with you, as another beloved member of the group says;-)

Always make sure valves are right as they can produce all kinds of weird symptoms. I'd also check for an air leak on the intake before diving into carbs.

The fact the bike has a higher mileage is an indicator it was used, it's usually bikes that stand for 10 years that have all kinds of crap in the carbs

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Quote from: huxj500 on July 18, 2015, 05:11:24 PM
bike is full stock and trying to keep it that way. could bad valves cause this sort of issue. I also forgot to mention that it only runs at half or full choke.
how many turns out should the mix screws be

Yes can be a tight valve. If you keep running it that way and you'd have a burnt valve. And before you do a valve adjustment, please source the non breaking shims, instead of the Chinese breaking shims.
Cool.
Buddha.

Quote from: huxj500 on July 18, 2015, 05:39:15 PM
THANKS TO EVERYONES POSTS. GONNA TRY RESETING THE MIXURE SCREWS. WILL REPLY IF IT WORKS. THANKS AGAIN

Hey man,  I had a problem a bit like this. Was gummed up jets and float. Gave the carbs a good working over with some cars cleaner and it sorted it for me. Modern fuel seems to gun stuff up pretty bad. At least it did in Australia.

Good if you can get the bike running at a fast idle then squirt some carbon cleaner down the fuel line so it makes it in to the float bowls. Should help.

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I would check your valve clearances before messing with the carbs.  I had similar problems when I got my GS with under 10k miles and it was due to the previous owner not ever adjusting valves (all were stock and I had unmeasurably small clearances).  The bike wouldn't stay running without at least half choke, and even then would often die when I was stopping unless I slowly reduced the throttle.  It took forever to warm up, too.

My best guess would be that the original owner did not keep the valves in spec and tried to compensate by adjusting the idler.  Mine has been running since late summer last year with slightly high clearances and I've had no problems.  She warms up predictably, idles predictably, and runs fine.  Opening up the valves gave her a more throaty sound, and also increased valve noise (which I really couldn't hear before).

ok tried resetting carbs and to no surprise it did no good. going to check valve lash tomorrow and adjust if necessary. if  I get my shims from a dealer can I assume that they are the non breaking. if not where can I find good ones

Quote from: huxj500 on July 24, 2015, 04:13:39 PM
ok tried resetting carbs and to no surprise it did no good. going to check valve lash tomorrow and adjust if necessary. if  I get my shims from a dealer can I assume that they are the non breaking. if not where can I find good ones

K&L - the breaking shims are sold at my local dealer. There is a way to spot it, some type of different lettering.
Cool.
Buddha.

Ok. I'm back with yet another issue. adjusted valves in which only the right cylinder was tight. now the bike will start right up at full choke but as soon as I release the choke it dies and if I leave at full choke and just slightly give it throttle it dies. any words of wisdom starting to become desperate as this is my only means of transport now

Quote from: huxj500 on July 26, 2015, 02:03:51 PM
Ok. I'm back with yet another issue. adjusted valves in which only the right cylinder was tight. now the bike will start right up at full choke but as soon as I release the choke it dies and if I leave at full choke and just slightly give it throttle it dies. any words of wisdom starting to become desperate as this is my only means of transport now

That was my best guess.  A few more questions to help us/you to further troubleshoot:

Do you happen to have your current clearance measurements handy?  Were your gaskets in good condition?
Have you tried adjusting the idler screw again since changing the valve shims?  Are you fairly certain that whatever you did to the carbs didn't change anything?
You also mentioned resetting the mixture screws, so that might some looking over.

Exhaust is at 0.083  intake is at 0.065. Tried tweeking the mix again and nothing still.