I have an '86 that i bought a few months ago.

It's never really run perfectly yet.  When i first got it, it stalled a lot.  

So, i took apart the carb and cleaned the heck out of it.  Definately ran better.

But, now it does something odd.  If i sit at a traffic light, it will idle perfectly for over a minute, maybe even 2 minutes.  Then it will start to bog down and, if i don't give it some gas, it will stall.  

I can restart it, but it will run like crap.  Then, the light turns green and I pull away.  Come to the next light, and the process starts all over again.

But, it only happens sometimes.  Sometimes I can stop and it will idle fine.  And sometimes, it idles crappy.

I think it blows a little black smoke when it idles crappy, so I'm thinking it's running rich for some reason.

Something sticking in the carb?  Why only sometimes, and why will it idle fine for a few minutes?

sounds like the fuel needle valve,there may be dirt holding it open or the o-ring might be damaged. imo.

is the float ajusted correctly?

Is it a little rich?  Any black smoke at the exhaust?   Try turning in the air mixture screw just a bit to lean it out.  Check your floats.  Also make sure your idle is correct.....

However....don't add any oil to your gas.  Ever!!  That is just an old school trick with a worn out engine.  It never lubes anything important and just dirties up the combustion chamber, plug and pipe.  

ALL the oil you need is already being delivered by the oil pump in all the correct places.  It is called a gas tank for a reason and the Savage ain't a 2 stroke  

Figured I'd add a little info to try to clarify.  

I'm pretty positive my idle and mixture screws are adjusted correctly.  95% of the time, my bike runs exactly like it should.

When i sit at a light, many times it will idle perfectly.  And, it will pretty much always idle perfectly for the first few minutes.  

But, every once in a while, after idling for a few minutes, it will be like someone flipped a switch and it just bogs down, trys to stall, and runs rich (black smoke).  

I work the throttle to keep it running, and pull away from the light.  When i get to the next light, it's running perfectly again . . . for a minute or two.

When i took apart the carb, the slide looked pretty worn.  Definately not black (is it supposed to have a black coating?).  It looked like raw metal.  But, it seemed to slide fine.  Didn't see any tears in the seal either.

I dunno.