Could I be lean?
 

I'm very interested to learn about jetting. I just installed a q4 slip on, uni filter, kdx snorkel, and a bill blue 33-34 pumper carb. I ride mostly around 6500' but will ride lower elevations often.
I got the carb installed with a 137.5 main and a 40 pilot per bill's recommendation. He also gave me a 37.5 pilot but told me to try the 40 first. The bike fired right up but had a backfire when I snapped the throttle. I could actually see a small flame coming out the exhaust. I started 2.5 turns out on the mixture screw. When I quickly but smoothly go to wide open it is smooth, quick and powerful. But when I snap the throttle it will hesitate around 7500 rpm. It has a backfire between shifts that seems to get better when I make the mixture richer. But another half turn and it will stutter on a quick acceleration. I have tightened the exhaust so I don't believe it is an exhaust leak.
Any ideas? I have tried to figure out what the pilot does vs the main but I'm not clear on it. I would like to be a bit rich at 6500' so that I have the ability to go down in elevation and still not be too lean.
All that being said I feel like I have a new bike! Fast, responsive and twice as powerful as stock. I can't stop smiling. I think I'm close but am I too lean?

Usually around age 40-45, after a few years of beer drinking and a desk job, you begin to get this protrusion from your midsection.... Until then, you're probably running lean.
:D :D

Funny. I really would like to know what people think. Please Help!!

Pull the airbox lid off completely. Take it for a run. Did that make it worse? If yes then fatten it up. Report back

Got it! It was one of two things or both. I rechecked header bolts and was able to tighten them a tiny bit. I also capped the line that comes out of the smog filter to air box. I had capped air box side but not the filter side. My mechanic friend told me that it would have no effect whatsoever but I capped it anyway. Not sure which of those two worked bt at 2 turns out the bike is snappy through the whole range with no backfire or decel pop at all. It is exactly the bike I wanted! My mechanic friend said that I should just leave the smog filter in place to breathe the crankcase. I've seen the link about removing the whole thing and just capping the crankcase tube. What do you guys think? Can't believe Kawasaki doesn't just sell the bike with the pumper carb. It is a totally different bike. Thanks for the input!

On why it doesn't come with a pumper carb, I'm thinking it wouldn't meet emissions requirements...perhaps.