Typically, backfiring on the savage is caused by an over lean idle mixture adjustment.
And/or either a loose header or muffler clamp.

Also most go up in size rather than down for improved performance.

When does it backfire?

On shut down?  is it a pop or KERPOW?
adjust the mixture screw CCW about an 1/8 turn to a 1/4.
be happy when it's a poof.

During shifts?
check the header bolts and muffler for leaks
a lit candle flame will flicker when near a leak.

The bike is definitely lean!  It  backfires both on shutdown & while riding when chopping the throttle.  I've taken it as far as possible with the adjustment screw.

What is the jet size these bikes come with?  I thought the 142 was a step larger?  Then go to a 145 if putting a new exhaust on.

Thats great about the petcock, thanks.  I'll just drain the carb & be good to go!

S.

Sharp, due to different years and models, you may take the original jet out first and read for youself what you exactly have in there. The size is etched in very small print around the thick slotted part. Only then buy one size larger. My stock one was 135.

Cool.