Need help with carb

Ok so my 2008 kx250f has a lot of low end power but when you rev it it bogs I have to roll on the power it also backfires a lot when I let of the gas i just can’t put my finger on what it is if anyone can help me out I would greatly appreciate it. And it has a big bore kit in it I believe 269, a fmf powercore4, and hot cams.

Sounds lean. Did you change the main jet when you put the big bore kit on? What size is in it now?

I second that it’s lean but since it bogs on the snap of the throttle my guess would be the pilot jet is too small or accelerator pump circuit is bad, I’d start with turning the fuel screw out and see if it gets better

I second that it’s lean but since it bogs on the snap of the throttle my guess would be the pilot jet is too small or accelerator pump circuit is bad, I’d start with turning the fuel screw out and see if it gets better

I bought it with the big bore kit in it and how far do u think I should back it out

I bought it with the big bore kit in it and how far do u think I should back it out

Go out half a turn and ride it, then go another half turn and ride it again taking note of any changes in power and once you get close you can dial it in with smaller turns
If you end up more than 3 1/2 turns out you need a bigger pilot jet
Should also mention that the bike needs to be completely warm before you test it

The fuel screw has nothing to do with this. Raise the main jet needle - goto second clip from the bottom.

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