I personally think it has all the effect in the world on carburetors.  About all one can hope for is to dial it in to a happy medium for most weather/atmospheric conditions and just let it go at that.

I will say this though.  After adjusting my valves the other day, whatever leftover pops are now gone.  So, I have a theory that even correct valve settings have a bearing on not just performance, but backfires.

Right now, I'm at a 52.5 pilot jet and 1 1/2 turns out.  I've been there before and had no success.  All I can say is that I kept plugging along the exhaust gaskets, the intake/exhaust boots on the carb, vacuum line, and all of that stuff until I finally got it.

I rode home this morning and it was very foggy and humid.  No backfiring.  The last few days it has been pretty dry humidity-wise, no backfires either.

Only thing I can figure is I finally got lucky.  My best midrange is coming from my spacer shaved to about 1/3 thickness.  No sooting at the muffler, no black smoke when I roll off the throttle.  No surging or hunting in the midrange either.

A week or so ago it was suggested I go thicker on the spacer, but that only made it worse, so I thinned it down more and it took that surging/hunting all the way out.

I set my valves at a loose .004 all the way around and the bike seems to just be breathing better.  I hadn't taken the time to get into them since I had just bought the bike in February, but they were really snug.  I didn't gauge them to see just where they were, but I would venture they were at low end tight spec or maybe a bit tighter, so it's a good thing I caught them now.

My fuel mileage is running between 50-52.  Thinking back on everything, where I used to get 54-57, I truly think that reduction is coming from the NC Dakota shield I put on.  It does drag more than my Street Shield did.  That, and I'm sure I'm a tad more aggressive on the throttle since I've accustomed myself to the Savage.