I have all the usual mods and have a klx300 FSW header. was thinking I should by an aftermarket muffler and hook it all up.......what kind of power gain could i expect.......just wondering if its worth spending 170 bucks........dont really want the added noise, just power

 

Not to hijack a thread but speaking of quiet + power, has anyone done an FMF Q4 review?

 

If you're looking for more power, there's really no getting around the exhaust issue, because increasing the flow is where you have to start from. None of the other power increasing mods -including big bore kits- will work properly without it.

You will gain in the neighborhood of 3hp from the combined effects of letting more in the airbox, re-jetting and adding an aftermarket exhaust.

The FMF Q4 makes good power and is quiet compared to the other available aftermarket options.

 

Yup Tremors correct at approx 3hp, and a little more with the head pipe addition.
I'm running the FMF P-Bomb head pipe with a HMF slip-on with a quiet core insert. It all work VERY well together. (all the other std mods as well)

As for quiet, bith FMF and HMF are right at 95db +/- a db.
The 95db range is still a bit barrky imo but it's the only way to get it to run as a true 250 should.

 

In terms of numbers that equate to HP gains, that can be debated all day long and frankly its like...beating a dead horse.

However in terms of what it feels like to those of us that have done the jetting and pipe mod....well that in my opinion is almost indescribable. I have been known to get more than excited when describing the power transformation on my bike. To me its night and day. Like someone strapped a nitrous bottle on my bike but didn't tell me. See there I go again, getting all excited about how my bike has turned out. And if I could let every member on here ride my bike to see the absolute difference I would. Now someone get out there and invent a machine that can transport you anywhere in the world in 5 seconds and get up here. OK what the....where did that come from. And I'm only on my first cup of coffee.

 

I really enjoyed riding my stock bike around town last year. Getting the KLX and my motorcycle endorsement were definitely some highlights of 2008.

The next logical step is for me to bolt on a Two Brothers or HMF pipe and install a DynaJet kit. Not sure if I can justify the P-Bomb right now.

I hope it gives more "seat of the pants" acceleration. An aftermarket pipe goes with the MX style of the KLX anyway, and I like to wrench on stuff.

 

Power gain wasn't what I was looking for when I spent $287. for the Q4 - weight savings was. I already got all the extra power out of my KLX250S with the airbox, carb jetting, and drilling out stock muffler changes. The Q4 weighs about half what the stock muffler weighs. I was impressed with how "quiet" the Q4 is. It's not like the stock muffler in dB, but it doesn't have an offensive bark like the HMF and some (almost all) of the others. When will everyone get it that one of the reasons we're losing access to public lands is the sound issue.

BTW - Do a search for carb jetting then get OEM parts for the carb rejet. You'll save a bundle over the cost of a Dynojet kit. Three main jets, an air (idle) jet, new needle jet w/clip and collar - all OEM parts was around $45.

 

Was VERY pleased with my bike after my jet kit and FMF Q4 were installed. I felt like the bike was much more responsive and the sound of the exhaust is not as loud as expected. You can open it up and it's loud, but with mild throttle control your neighbors won't be annoyed.( alot quieter than all the Harley guys!)Best mod. for this bike!!
I had my dealership order and install for me so as not to have any issues with warranty debates down the road. Was very pleased with how they treated me and they also gave me a discount on the jet kit and exhaust.

 

+1 on the NOISE issue, even on the street people are getting upset with the loud pipes.
I still have the HMF but last summer I modded the quiet core by completly blocking off the tube from the inside and drilling several .120" holes around the tube. worked out very well and kept it much quieter but still more than stock. It even got rid of the "bark" because your blocking or knocking down the sound wave that would normally shoot straight out the back. Actually this is how many procuction exhausts are done on the inside.
If I can figure out how to get my hands on a SS OE muffler I may even sell the FMF-HMF pipe/muffler and do a full stainless stock exhaust.

 

Thanks for the feedback on the FMF Q4. I like that pipe, too, but I thought it was louder.

I am basing all of this off of videos and sound files that I've found on the net...on further review, I started thinking the Two Brothers was too throaty and the HMF was more mellow.

If the Q4 is established as the quietest of the bunch, I'd consider the extra money to get that. I want the power and some tone, but I don't want to rattle windows or go deaf on my commute. (I often wear ear plugs on longer rides because of the wind noise.)

Good idea on the rejet parts- I basically know what I would start with as a baseline, so just getting those parts would save some coin.

I was thinking of getting one of those Kouba fuel screws, but I am such a tweaker I think I'd be fiddling with it all the time.