If the engine pulls smoothly at light throttle settings - I would not change the spacer to alter the height of the slide needle.....that has nothing to do with the noise you get with a closed throttle.

Is the popping and backfiring only when decelerating with a closed throttle or as you shift gears?  If so.....try raising the idle speed a bit.  Also don't allow the throttle to close completely when coasting - just move your throttle hand a tiny amount more open until the noise goes away.

Seipgam wrote on 06/01/21 at 02:38:58:
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I'm thinking a 55 pilot is going in the wrong direction and 3300 ft of elevation.    Thin air is a real thing...I would probably be going to a 45!!  

I did check for air leaks and found none.
I'll list here a summary of jetting mods that I have done and the results of each.
Before I began, I just want to say thanks for everyone's advice. Much appreciated.
[url]What I started with:[/url]
- 45 pilot
- 145 main
- Removed airbox and installed a K&N cone filter.
- Change stock exhaust over to a long shot pipe welded onto the outlet of the header pipe and inserted a 13 inch baffle wrapped in exhaust packing.
I am getting a lot of popping on deceleration along with a bit of not extremely loud backfire. It seems a bit sluggish in the midrange but improves slightly if the choke enrichment is pulled out to the first notch. Currently I have the idle mixture set at 3 turns out for the highest idle speed point. It doesn't seem to change much (maybe 50 rpm) from 2 to 4 turns out.
Fist carb mod:
- 50 pilot
- 150 main
- 1/2 spacer
I think the main jet change to a 150 is probably perfect. Good steady power on the throttle. No surging and no harder pull when I roll off the throttle.
- I achieved my best idle at 1 3/4 turns out on the idle mixture.
- I'm still getting a lot of popping when I roll off the throttle hard. I don't mind a bit of popping (actually kind of like itSmiley) but the frequent backfire is annoying. There has got to be a further alteration to eliminate the backfire. I tried turning the idle mixture out another 1/2 turn to 2 1/4 turns. Even though it smelled rich it made no difference in the popping or backfire.
Second carb mod
- previous change to 150 main kept
- previous change to 1/2 spacer kept
- change pilot from previous 50 to 55
Could not get a good steady idle no matter what the idle mixture setting
Third carb mod
- previous change to 150 main kept
- went back to previous change of pilot of 50
- changed previous 1/2 spacer to 3/4 spacer
- achieved best idle at 2 out
This was a wee bit sluggish at low rpm. Still lots of popping and some backfire. Max speed 134 kph or 83 mph. 80 to 100 kph (50 - 63 mph) time 5.5 seconds
Fourth carb mod
Went back to first carb mod, 50 pilot, 150 main, 1/2 spacer
Better power, smooth mid rpm power, not sluggish, Max speed 138 kph or 86 mph. 80 to 100 kph (50 - 63 mph) time 5 seconds
Still frequent backfire when up shifting throttle release. Tried richening up the idle mixture to 2 1/2 turns but mad no difference on backfire so went back to 2 turns out.
I think this is the best it will get. So as Dave has suggested, try and ride in a fashion to reduce backfire. (Don't roll off the throttle fully.

If anyone wants to see my bike "Covid Bob" you can check out the black bobber on this page replies 1076 to 1079:
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1290745273/1065
Thanks everybody.