I need to get out some info regarding the performance carb for the Savage/S40.

There have been some folks who have had some difficulty with the jetting on the carburetor, being too rich for their setup.  It seems that the exhaust systems/mufflers being used on the bikes are too restrictive for the amount of fuel/air that the carbs are supplying.
It is the old problem of too much in, but not enough out.

I want to be sure everyone understands that when swaping out the stock carb for a performance carb, it is necessary to have a FREE FLOWING EXHAUST SYSTEM.  Mufflers like the screaming eagles, Mac, Jardine, Supertrapp with plenty of discs, and some of the sporty/dyna tubes.  BUT, there are also some of those stock HD mufflers that have been showing up and are proving to be too restrictive.  I do not know yet which specific model year HD mufflers are the ones to avoid....perhaps a few of the folks who have recently installed the carb kits and have had the OVER RICH situation could post a note about which muffler they had initially.

The bottom line is that when installing a performance carb it is also necessary to have a performance capable exhaust system to keep the air flow going from beginning to end.

I am not a big fan of drilling on the back end of a muffler, it usually offers little to no effect when it comes to jetting on a significantly more capable performance carb.  This particular issue of rich mixture requires more airflow than just drilling can provide.
When a muffler is too retrictive then the only productive thing to do is remove the baffle, which may or may not be acceptable performance wise, or replace the muffler with another one that is a better match for the new intake/fuel system.
This is a balance thing...if you want more fuel/air to come in for better performance, then you have to be able to get more exhaust out in order to realize the potential of the "whole system".

You are correct, altitude will affect the jetting.  One main jet size for about 3-4000' if I remember right, and temp/humidity can also affect it but not quite as much as the others.

With that said, my primary point for the post was to address a common issue with restrictive mufflers when making the carb swap.  Not every "other than stock" muffler is appropriate for the performance carb upgrade.

my 38mm is till not jetted right, but I like the backfires. I CANNOT find the sweet spot on the pilot.  and the main works great going uphill, but sputters on a flat road.  I think I have a float issue.  Stock carb is jetted dead on with the same pipe.

At any rate, my point is that tuning a carb can be a long process, esp if yr. lazy (or drunk).

V