No air box lid

It sounds like a jetting issue. Do you have the stock jets in your carb?

This helped me a lot. 2012 Carb removal and jetting with jet part numbers!

I’m running a 165 main 47.5 pilot and I have ordered a 170, 175, and 180 main jets to try out I also ordered a 50 pilot to see if it helps at all

with the jets I have in it now I turned the a/f screw out 4 turns (I know it’s a lot) just to see and it made a noticeable difference on the backfires

The 50 pilot jet helped mine a lot.

I take it you had the same issues as I do with the backfires?

It backed fire some but not too much. My main issue was that it wasn't running good at full throttle. I removed the air box lid and it stopped.