I have a 2012 klx with no performance mods done until today. I finally put on my FMF Q4 that's been sitting here since March. The last pipe I put on a bike was in '74 on my 250 F11. Of course I didn't get the gains from this slip-on as I did with the expansion chamber back then. I was debating and researching the install because I really don't want to mess with the jetting. It was really nice to ride a bike that didn't sound like a sewing machine. Love the sound and seems like much better throttle response. The install was very simple and couldn't be happier with it. If I can stay away from rejetting I would like to add the Powerbomb. I ride mostly street and back roads so I don't think I'll be making any more mods.

 

If you're going to add a header you might as well open it up and rejet. Then you'll have something a little more noticeable.

 

I am not carburetor savvy so I really don't want to rejet. Can I add the header and not rejet? I don't want to run too lean and ruin the engine.

 

This is a good bike for becoming carb savvy. Very simple and it's a crime to not rejet ... even without a new exhaust.

 

If you have fitted the Q4 you are lean already

 

Call FMF see what they say as they'd be the experts for that one. On my bike the stock jetting was spot on with a powercore4 added, I jetted before the powerbomb when I changed the airbox, but if you left the intake side stock it might be fine. The powerbomb made no issues with the jets I had in before the swap.

 

+1 if the intake is still stock you are probably ok

 

Honestly, if you buy the dyno jet kit, it will come with instructions on how to do your rejet and it is fairly simple. I think the hardest part is just taking the carb out and then back in. Rejetting is the easy part!

 

if he reads the Signatures of people he can get a really good idea on the carb setup

my Q4 is only 86 DB

 

My Q4 has tested at 96 and even 97 dB once. For crying out loud it says 96DB right on the muffler. You didn't get 86. I like the sound but at times wish there was a god way to bring it down a bit.