I just found this forum!  Looks like a great place!  And hopefully somewhere here can help me narrow down the source of my problem
I just purchased a 1994 Suzuki GS500e.
When I got it, it wouldnt idle without the throttle part open. So...from my background with carbs it seemed obvious that the idle circuit was probably plugged (had been sitting for a couple years).  That said....Im much less familiar with powersports carbs than I am with automotive carbs.  At this point, I haven't tried to rev it at all, just started it and held the throttle enough to keep it running long enough to make sure the engine and etc seems fine before purchasing it. 
I got it home, pulled the carb, and stripped it down.  jets arent obviously obstructed, float needle tip is still nice and soft.  Cleaned out everything real well, blew out the jets with compressed air, carb cleaner on everything, just your typical carb cleaning. replaced a few o-rings that were hard as a rock, and the float bowl gaskets.
Put it all back together, and now it seems to idle pretty well. 
I should also note I put brand new plugs in it.
But there are a couple of problems I'm having:

1. if you barely open the throttle the engine will gradually increase speed, smoothly as you would expect it to.  But if you turn it probably about an 1/8 of a turn or more, it bogs down hard and takes a few seconds to catch up before it will increase RPMs, and even then it seems to have a hard time revving past 5-6k without doing it very slowly.
2.  It seems to be very slow (as in several seconds) returning to idle once you get the RPMs up a ways and let off the throttle
3. If it is at idle, warmed up, and the choke is ON, it normally runs around 3500 to 4k rpm.  but once in awhile, without touching the throttle or anything, it will speed up to 5 or 6k rpm and stay there.  Again, this part is only with the choke ON.  w/ the choke off it idles nicely around 1k to 1500 (not sure where proper idle speed is, so havent adjusted this)

Probably important to note that it has a K&N air filter.

From all of the reading I've tried to do online, it seems to point at the jet needles as the issue.  There is only one groove/position for the clip, so i tried shimming and that didnt seem to change much. I shimmed them a little at a time, up to as much as 1/8" (maybe that isn't actually very much....I can't find any info that says how much one should shim them to account for a lean condition on part throttle)  Far as I can tell it's very lean or starving for fuel.  Running the petcock on PRI doesn't make a difference so doesn't seem to be a vacuum or petcock issue.   needless to say, I'm at a loss.  My experience with motorcycle carbs is minimal, and they are quite a different animal than the holley's and edelbrocks and etc that I'm used to on my vehicles!  Any and all input is appreciated.  I'm really hoping to get this running nicely so I can ride it a bit before it snows!!

Thank you in advance!!

Welcome to the site man!

Your description in #1 sounds like your float level is too high (too much gas). And did you make sure the carbs were jetted for the K&N?

#2 sounds like an air leak around the intake. Usually dry boots / orings between the carbs and cylinder head.

#3 points to an air leak as well.

Thanks glad to be a member! And thank you for the info.
What measurement should the floats be at, and between what two points should the measurement be taken? I'm not too familiar with particulars on bike carbs.
Also, what are the factory jet sizes and what should the be changed to for the k&n? Bike is stock otherwise.
Intake/carb boots all seemed ok at a glance but I wasn't inspecting them. I will look over them real well in the morning. 

I think you have a clogged pilot jet.
Its supposed to have 122.5/37.5 from the factory.
What K&N filter ? The one in the airbox ? Then 40/127.5.
If its the one replacing the airbox, I'd do a slip on or pipe - and then it needs 40/150.
Cool.
Buddha.

Now this is a thread that I may need. . .

Excellent!

The K&N is the style that replaces the air box.  It currently has factory exhaust, and I can't afford to purchase aftermarket at the moment.  What jet sizes should I have with this particular K&N w/ factory exhaust?  I will be check current jet sizes within the hour.  Will also pull the primaries and re-clean them to make sure they aren't obstructed.

Ok, current jets are 122.5 / 40

People have tried and liked 142.5 mains. I have not run it myself, so I'd defer to that.
Set your floats right and make sure all fuel passages are clean.
Cool.
Buddha.

Ok the carb boots were leaking.  Seals were hard as a rock on the intake side and starting fluid sprayed at the base would increase rpms. On the carb side the boot was nice and soft, no cracks or anything. Put new orings on, now no leak. Air filter boots are also nice and soft woth no cracks or obvious signs of wear. Set floats to 14.6mm (gasket surface to top of float per spec that I found on gstwins wiki. Double and triple checked all passages and jets etc. Everything is as clean as a whistle as far as I can tell it  anyway. Fired it up and zero change.  Still bogs really hard with more than about 1/8 throttle.  If I can slowly work it up over 8k or so it will *sometimes* Rev out nicely from there but not always. And when it does it pops hard on decel. When at dead idle if you go to 100% throttle it will typically drop rpms and sometimes far enough to kill it. Sometimes it will raise up to 2 or 3k and then hesitate and go up and down about 1k and pop. It's really confusing the crap out of me!!  Is it a reasonable assumption that my jet size being a bit small is not likely to be enough of an issue to cause such a severe problem by itself?

Try checking the float height with the tube method if your willing. I tried measuring mine off the bike and ended up being horribly off from what I thought was right on. Also I thought on all carbs in general, that they bog down hard if the throttle is snapped open at low RPM.  I wish I could add more. I'll be keeping an eye on this one.

Thanks. I will check that. Both of my quads and my other 2 bikes are very responsive to snapping the throttle. But that said, this one bogs down even if iIslowly open the tthrottle about 1/4 of the way. 1/8 is fine, after that it just falls on its face. It's like as soon as the idle circuit is no longer in the picture it just can't keep up.

That is one finicky throttle!

I'd honestly save the money and buy new(er) ones and burn the old ones while walking away in slow motion. . . 

But sometimes persistence is the key!