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Posted: **11:10 pm Sep 09 2025**

Thanks for the info! I like quite like Pro Circuit's products, and if they still made an expansion chamber for the E series I would have bought one.
I think I might go with the Nature Friendly silencer. I don't ride in national forests but if I ever do it would be nice to have (apparently the Forest Service likes seeing the Forest Service approved marking), and on top of that it has a spark arrestor, which my current FMF one doesn't have. The fact it's quieter is nice. My current silencer is definitely quieter, or was anyways, than my CR125, which was always a plus for me, even though I love the sound of 2 strokes, loud pipes tend to work against you.
Personally I think it looks nicer than my FMF one as well, so that's nice.

Thanks again!

Edit: I'm hoping to make it up to Wellsville this October before it gets too cold. Currently am working on getting my 92 running right with a Lectron, I'm getting there, so hopefully it'll be done soon.
That place was a blast, I'm going to have to try and find the trails you were talking about, as my father and I were just farting around getting lost!

Posted: **09:53 pm Sep 26 2025**

I have the "Nature Friendly" on my e-series. It's very quiet. You'd like it. I used some high temp radiator tubing to cover where it joins to my FMF pipe, and that helped silence it a bit too (just because it wasn't vibrating against the frame). It hasn't melted yet.

Posted: **10:45 pm Sep 29 2025**

HeyItRuns wrote: 09:53 pm Sep 26 2025 I have the "Nature Friendly" on my e-series. It's very quiet. You'd like it. I used some high temp radiator tubing to cover where it joins to my FMF pipe, and that helped silence it a bit too (just because it wasn't vibrating against the frame). It hasn't melted yet.

Thanks! Mine just came in the mail yesterday, I'm hoping to get it put on this week. Glad to hear you like it! It certainly looks very nice.

Posted: **01:37 am Oct 02 2025**

Here is the SR model muffler if anyone is interested, doesn't appear to show anything about the spark arrestor like the R model does so now I know why the part numbers are different even though they look identical

Posted: **06:58 am Oct 08 2025**

kdxdazz wrote: 03:10 pm Sep 01 2025 The KDX250SR is a chambered design, the first part is a resonator wrapped in fibreglass, the second part is the chambers, very complicated in design.

The mounts don't bolt up at all to the H series, I had to cut off one ear and reweld it in a different position and made an offset mount for the other one.

I bought it not knowing it was missing the chambers but I brought it back to Australia so I could make it fit the H series then back in my bag it goes back to Thailand, I have another kdx250sr muffler lined up to use the missing chambers

I don't believe there is any spark arrestor

Part of noise suppression in the expansion chamber is the thickness of the material, so there is no way around it, heavier and quieter or not.
The weight on the stock pipe compared to aftermarket really is negligible given the weight is carried low but like you say the procircuit has an incredible midrange hit compared to stock, I prefer stock for it's off idle performance and like you say the procircuit just seemed to wheel spin and break traction which made it exhausting to ride.

I'll test the kdx250sr muffler using the wideband O2 sensor so I can see what jetting changes are needed

kdxdazz, did you ever get the time and 250SR muffler parts to assemble it and test it?
I've now got one in transit from Japan for around $100 USD shipped w/tarriffs included.

I'm wondering about their internal construction. Is the chambered portion at the front/bottom? That's where the oil drain hose nipple is located. So you're saying that part of the muffler is a typical fiberglass wrapped perforated tube type baffle, but the other part is chambered? Do you have any photos of the chambered portions?

I'm slightly concerned that the chambered design may choke up the top end power a bit due to slowing down flow.
BUT...,[/I] as I have 2 KDX220R bikes & 3 total engines (1 spare), I'm thinking this winter, I'll build the 3rd engine up as a KDX220R low/mid torque technical singletracks build that won't target maximum top end revs, so the chambered SR muffler may be perfect for this, paired with an FMF Gnarly Woods pipe or the stock KDX220R expansion chamber.

The trials/tractor-like 220R engine would include :
* my ported 70mm 223cc big bore cylinder (as long as the port timing measures out to be stock still,
* modify 1 of my 2 KDX220SR heads from stock 69mm bore to suit the cylinder's 70mm bore, while also opening the head chamber in the lathe to slightly more total surface area removed than what's removed from the outer 0.50mm to enlarge the bore, as to keep the extra wide 220SR's squish band total area the same as the stock 220SR head or perhaps just a slight bit less (this head profile will definitely boost low end power significantly vs stock or RB'd heads but will compromise top-end considerably)
* 13mm KIPS resonator chamber spacer (milled out of 1/2" billet aluminum plate + a 2nd gasket) (to boost the low end torque prior to powervalve opening/subports closing off the resonator chamber)
* FMF Gnarly Woods pipe or stock 220R expansion chamber (if my OEM chamber is repairable)[/I)
* Static ignition timing on stator plate (w/stock CDI) advanced near maximum, & only backed off slightly if the low-mid throttle response is too touchy.
*PWK33 stock 220R carb -or- 34mm Lectron Legacy power jet carb -or- perhaps a supermini 28mm flatslide carb if I can find a PWK28 to adapt up in spigot/airbox bell size to test.

This should make an interesting winter 2025-2026 experimental build - the quietest exhaust I can assemble for the 220R along with a very low/mid torque focused engine...
I think the stock pipe may perhaps be better than the FMF Gnarly Woods pipe for 5000-7000rpm range power, as it's the closest in shape to the Pro Circuit, but having more grunt off-idle as you report. Mine is quite banged up, but with oxy-acetylene & brute force + technique as well as pressurizing to blow out the dents from the outer layer, I should be able to rehabilitate it I'd hope. & The Hyde Racing pipe guard skid plate combo *may* potentially fit the OEM pipe, whereas the FMF Gnarly Woods pipe absolutely does not fit the pipe guard skid plate combo designed for the FMF Gnarly Desert (the Pro Circuit pipe does also fit it somewhat decently).

Posted: **08:15 pm Oct 08 2025**

That sounds like some great projects you have, glad you got your hands on the SR muffler, the very last part is chambered, the part near the mid pipe is the resonator wrapped in fibreglass, I have a disassembled photo of the SR pipe somewhere on my phone, will try to find it

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Quieter exhaust options?

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