I bought'n Pikas' exhaust..
His For Sale thread - https://www.kawasakiforums.com/forum...-klx250-44246/

So this is what I bought:
"FMF Q4 muffler (042173) and Power Bomb header (042155) for 2009 KLX250"

I just slap'd em on my '07 KLX300R, taking off the stock header and silencer(which has its' tail-end Butt Plug off/removed..)

Impressions:
The Q4 is WAAY mo quieter than the stock (uncorked) silencer!
Unexpected this is..(Yoda)
Performance-wise, it still pulls crazy power wheelies in 1st, 2nd, (and 3rd with a little tug-o-bars..) so I don't know yet if top end has "opened up" - so more to come..

I have no idea how anyone could think a Q4 is loud - Compared to my PC4 on my KLX250S, it is downright wimpy sounding! I'm kinda hoping that removable spark arrester stuck in its' tail is actually also a sound reducer.. I got a good mind to yank it outta there..

 

Well, the top end does not feel "opened up" .. On pavement there is a distinct slackening of power as RPM's reach redline, in the upper gears, with a snap-and-hold WOT from midrange RPM's..

The power ramping and levels in the mid-uppermid (perhaps 5k - 8K) is very impressive and resembles the surge of a racing 250 (4 stroke)..

My carb setup (Lidless,DJ146/3N with 2206 kit) requires revamping due to the new information we have from Houstons4's Dyno data.. So, while I perceive no fueling issues, a reset to 1N is certainly called for..

Now that I have the stock 300R exhaust off the bike, I'm going to look into its' actual measurements.

 

Good info KLXster.
I find the klx 300 can to be annoying with the end cap off.
I made an aluminum cap with a 1.25 hole in it.
Mellower, but probably sacrificed hp.
I'm ok with that.

 

I'm thinking that you aren't sacrificing much. With the stock header and a lid - even with a larger hole - it looks like they will run out of flow before the silencer..

This is from analysis of our latest data from Houstons4 dyno charts..

Your bike probably pulls hard to 8k tho...?

 

Over the weekend, I was able to ride the KLX300R a little more.. Without a tach, I can't really tell where the power begins to taper off way up top in the RPM's..

I also was able to measure the exit on the Q4..

PowerCore 4 - 1.5"
Stock KLX300 can - 1.375" (1 3/8") This is with the stock end cap removed.
QuietCore 4 - 1.4375" (1 7/16")

 

I tried my Q4 with the standard insert and it was just too loud for my preference. I put a quiet core tip in and it is still pretty dang loud for playing around the yard (I live in a subdivision).

If I lived in the country I probably wouldn't give a hoot and would run the larger tip.

 

Well what would be interesting to know is how much, or how little, a Q4 with a restrictive tip offers in performance over the stock silencer. For a bike that must be kept at or near stock sound levels, it could be that a DJ2152 kit + stock exhaust performs very closely to same + muzzled Q4. The stock exhaust carries a smaller midpipe - which promotes TRQ below 7k rpm. The Q4 has a larger dia. midpipe that would tend to raise, perhaps extend, TRQ a little, but higher RPM TRQ tuning also relies on unrestricted flow.. Anyway, just thinking out loud since the Q4+Quiet tip is a significant "chunk of change"..

 

Reset the KLX300R's DN0352 needle to 1N - It was on 4N !!!

Rode it on the ranches' road (pavement).. simulated dyno runs, engine only wheelie test, etc... I suppose I like the results - power ramping is ultra "smooth" .. no discernible variances in thrust as the engine revs up @ WOT - just even, smooth, thrust.. Power only wheelies in 1st, 2nd, and 3rd gear are easier and happen quicker...

Mo ridin tommorrow..

 

More time on it today.. No change in assessment.. With the bike now more quiet and with such a smooth power delivery, I tend to think I have less power - Thank goodness for the 1st gear wheelie test.. The fact that the bike will now "loop" out from underneath me if I don't keep my right hand under MY control (Instead of all those voices..) cannot be ignored..

So, it stays "as is" - Lidless, 2206 kit, clip on 1N, DJ146 main jet, FMF Powahbaum + QuietCoar 4..