Long time listener - first time caller here...

I am riding a '95 savage with stock everything except for:
~2/3rd white spacer
K&N drop in air filter

I just received Lancers jet kit.
I would like to run a bit richer for more power and less pipe color changing.  I also get a fair backfire when cold and down shifting / off throttle that I could do without.
What is the best jet combo with this air filter and a stock exhaust?

I would like to add a Dyna muffler in the future.
What is the best jet combo with the Dyna and the drop in?

Should I loose more of the white spacer with any of the above changes?

Thanks for any help.