Hello all!  I am a long time lurker here and have learned a ton from all of you.  I apologize for such a long post for a first post, but I figure no sense in just coming on and saying I have a bike problem.  I have an '86 Savage that I picked up for my first bike last year.  Since then, I modified the air filter in a similar fashion as Oldfeller spoke about in his Jedi thread, and also thinned out the white spacer and tuned the pilot screw per Lancer's recommendations.  When I put it up for the winter, it was running pretty good.  Of course, being a relative idiot, I didn't add any stabilizer to the tank when I stored it.
Realizing what I had done, I pulled the carb off 2 weeks ago and cleaned it out, and also drained the tank and refilled with fresh fuel.  The first time I fired it up this year, it idled roughly before fuel started flowing out the vent tubes on either side of the carb.  Figuring it was a sticky float or something along those lines (I ruled out a petcock/vacuum leak) I pulled the carb off again and found a small tang on the float that looked like it was supposed to hit against the towers, yes, the float was upside down.  Flipped it over and that solved the vent tube problem.
Put it all back together again, but this time I recorded all the jet sizes, as I had figured they were all stock, but just in case...
This is where I found out that the carb had been replaced, as it had the equivalent jets as a '95 stock mikuni would have, 45 pilot air jet, 52.5 pilot jet, 145 Main jet, with a 5C39 Jet Needle and an X-7 Needle Jet.  
So anyways, got the carb back on the bike, fired her up, and found that she won't sit at idle.  Period.  To keep her running, I need to keep the throttle open just a crack.  I have the idle speed screw in all the way, and she just stumbles and dies as soon as I release the throttle.  My gut is telling me that I need to rejet; I'm thinking that one of the passages might have been clogged and now everything is nice and clean and because I have a low resistance filter in, it's running way too lean?  Also, if I give it a couple good revs, it backfires really bad, definitely in the exhaust, not in the carb.  I also tried removing the white spacer completely, but with it like that she wouldn't run at all.
So any ideas?

I am positive I put that washer back in, but I will double check.  Lunch time here, so back to the garage to pull the carb off...again...
At least I'm getting pretty quick at it!

There's also some tiny idle passages on the intake side of the carb right near the edges of the throttle plate,... they flow constant and are not metered by the pilot jet... run the wire through them, too...
Spray carb cleaner through'em,... blow compressed air,... pray...
There's probably something, somewhere...  
...it only takes a speck to screw you over... ...

good luck...

Spray cleaner up through the pilot jet and any other holes down there, while watching those tiny holes,... and see if you can see fluid coming out from them...
Spray a lot....  you can get partial flow and still have blockage, that's why I try to get wires through them...