Suzuki LTR 450 rev, backfire and stalling issue (Problem solved)

Описание: Rev problem on my Suzuki LTR 450. I've been having this problem since I bought it second hand just over a year back. It's got a stage 2 intake hot cam in it, cherrybom and airbox open. I've adjusted the TPS sensor according to specs, valve clearance checked and in spec, fuel injector cleaned and tested. Why would it only do this sometime?

I'm losing time in my races in the pits when I'm switching the quad off to refuel and having this issue when I'm starting it again.

So here is what the problem was and how I fixed it...
First I checked my throttle body butterfly valve as the previous owner had a hand adjusting screw on it. I closed the butterfly valve completely and turned the screw just touching the valve and keeping it completely closed.
Then I adjusted the TPS sensor again to spec at 0.6 V.
Then I checked my idling air screw... It was turned out 3.5 turns. The manual spec is 1 5/8 turns out, which means mine was way too lean with the throttle body valve also a bit open. So I adjusted the idle air screw 1 5/8 turns open, started the quad and what do you know... it started easier, sound smoother, revs up with no issue and the abnormal backfire is also gone, just popping now and then on deceleration.
It's been 2 months since I fixed it and had no starting, rev or stalling issues. Seems like such a small thing that fixed about a years struggling with it.

Hope this could help some of you out there with the same problem.