New FMF
 

Just got my Powercore 4 and installed it love it. Nice and loud but is it normal for it to backfire when you slow down?

Yep. No baffling to stop it, just the way it is.

You can get some backfire relief by tweeking the fuel screw a bit to richen up the pilot circuit when you close the throttle. You may affect throttle response if you go too far. Good luck.

Did you re-jet?

Mine backfired ever so slightly on decel.

Aside from the air/fuel mixture screw did you follow the instructions for attaching it to the header. Your suppose to use high temp sealant and let it set for 24-hours before firing it up. An exhaust leak can cause that too.

Mine can backfire pretty loud on decel, especially on a cold start.
I does sound good though ;)

Just giving you a heads up on the Powercore 4 it WILL melt your airbox (Happened to me) so what I did is around where you join it into the header I put some exhaust tape to keep the heat inside of tailpipe. Just a friendly suggestion! :)

That really happened to you?
I have had the powercore 4 on the klx for over 12 months and had no such issue or even heard of that issue.

Really? Might of just got unlucky or something. The side of the airbox that is closest to the tail pipe near the joint is all melted up, not a huge hole but it's still a hole. I've had mine for, 10,000 KM (6000 miles?) with the Megabomb header. I'd post a picture but I can't seem to upload it.

That's odd, I've done around 4-5k miles and no signs of melting of the air box.
Did you bend the rear right foot peg mount outwards for a better exhaust fitting?

Then again I haven't added any head pipe I'm still using the stock header, maybe that's what has caused the melting...

When I had my FMF on it had a deep gurgle/rumble coming off the throttle, with a few good loud pops thrown in, especially if the run was WOT.

@ daren1093251
Stick a pry bar in there and gently pry the pipe out (while connected). Mine was touching, so I had to do it. I got plenty of room doing that, give it a try and then you can plastic weld your airbox and it'll be good as new.

Nope, I did a direct fit on my 2013. Maybe just bad luck or one day it got hotter then it should have.

Awesome, thanks for the advice. I never thought of that!

Rivet or JB a small section of Coke can to the bottom of the air box to act as a heat barrier if you need to..

I have a full header/pipe FMF..and just the tip of the airbox got a small melt on it.nothing to make me worry,hasnt got any worse...

My airbox melted as well, maybe a hole the size of a quarter. I tried to reposition the pipe unsuccessfully, but never used a pry bar. I just may try that then use plastic weld.

Slow steady pressure, then when it's far enough away, give it just a momentary bit of extra force. I mean for a millisecond, and you should be good to go. It's not about brute strength, but leverage.

If it is backfiring and popping on deceleration, you are running too lean. End of discussion. Now go and re jet for your new tail!

Not necessarily true at all. It's quite common to have a leak where the slip-on connects to the header.

If you find that you're melting your airbox, you might have a jetting (lean) problem.