Light backfiring ???

I installed a yz 450 cam a wile ago on my wr, altough I love the ease of starting and the power output, not less but a bit different output.

It tends to backfire after a short rest. It doesn't get cold enough to need the choke. The bike is an easy starter normally. But this backifiring at wide open throttle worries me a bit. Only slight popping on deceleration. But when I twist WO the throttle I feel slight backfiring for a few minutes, once the bike is hot it behaves ok. Elevation less than 2000 ft.

The air box snorkel is removed, no lid, YZ pipe, Zip Ty fuel screw, low restriction air filter (twin or unifiler), 450 YZ cam, Dr D. hot start.

Carb settings :

jet needle OBDQR standard position 4th clip, main jet 170, pilot air jet 75,

Thanks for your inputs.

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