If I only install the FMF Q4 slip-on do you think I still need to rejet? Do you think I should install the Powerbomb? I just do some casual trail riding and more street.

 

You shouldn't need to rejet with just the slip-on.

 

Jetting will prove to add the performance, not the pipe, the pipe lets more air flow, which means lean condition in motor, it is already lean from the factory. It is best to rejet

 

True you don't need too, but you should. Stock EPA jetting needs to go, a dynojet kit will help even a totally stock bike. At a minimum remove the plug on your fuel screw and back it out half a turn. Enjoy your upgrades!

 

The product insert that came with mine new (Powercore4) clearly said no rejet was necessary. These bikes are stranguled by the stock exhaust and all afr's on completely stock bikes I've seen were actually a bit rich so I believe you are safe without a rejet. I did my powercore4 1st and it added some much needed pep as stock the bike was a total dog and with it, showed signs of life. I then did the dyno jet it as I wanted to do a good ac and airbox mods. Really I didn't notice as big of a jump with the jets and the ac, and box mods as I did with the pipe alone. I then added a powerbomb and it was another small improvment and I no longer think it's a dog.

 

I forget where I read it but the '07 and older came a bit rich from the factory; the '09 and up come quite lean. I'd expect to have to rejet a '09 & up if installing a freer flowing exhaust.

 

I didn't have to rejet when I put just my Q4 on. But as soon as replaced the snorkel and air filter I did.

 

Thanks for all the responses. I am new to this with my 2012 KLX250. I would like a little more power without making too much noise and added upkeep. Brieninsac and linkin5 do you recommend I go with the Powerbomb. If so, I would assume I need to rejet if I go with both Q4 and Powerbomb? Do you recommend the KDX snorkel and what type of gains would it bring? Thanks for helping this newbie!

 

you should still adjust your air/fuel by drilling out the cap to reveal the screw....

 

Since u don't like loud, I have the q4 and its still loud, why not try 13t front sprocket change. Better response than a pipe alone. A lot cheaper too . Just right for occasional trails and highway