FE390 stock muffler good enough?

Wallander · May 14, 2014

For my FE390 I have the stocker restricted muffler and an FMF 4.1. Bike is EU mapped, ignition set to advanced.

The stock restricted muffler:

I have an insert in the FMF 4.1, but it is rather big in diameter and loud (I'm sure it's not the 94dB version), maybe you can see it in this image:

Comparing these mufflers, it seems the bike is NOT running better with the FMF at low/mid revs, and only slightly better at high revs. I also have an XR400 (now 426cc), and for that bike an open exhaust (FMF Powercore4) made a great difference at low/mid revs, but that is a very different engine, super long stroke compared to the super short stroke FE390.

So the stock muffler seems to work fine, and it is quiet, which is good for me, but it is running hot.

Maybe the FMF 4.1 with a smaller diameter insert would be better, to better suit the FE390 engine?

Many thanks.

akshun · May 14, 2014

Is your FMF 4.1 new? If not, could it need repacking? I cant speak for the 390 but i definitely felt improvement over the stock muffler when i fitted the 4.1 to my 570. Although i swapped the whole system so maybe that is why it had more effect? I agree that they are way too loud without the insert! I don't know how many size inserts are available but i do know the one that came with my exhaust quietened it down considerably! I didnt feel that it robbed any power having it fitted either! I would say that mine is a little louder than stock and definitely has a deeper note but it's not obnoxious. How loud is it compared to your other bike with the open exhaust?

Wallander · May 14, 2014

Many thanks for the reply. I've got the 4.1 used, but the packaging seems good, I've replaced much worse looking ones with almost no change in sound/performance. I've just ordered a 94dB insert, we'll see how it works.

The 94dB insert looks like this:

My current insert is considerably larger in diameter. What is your insert like?

I'm sure the open 4.1 muffler works great on your 570, as it has greater gas flow. I wonder about other 390 owners experiences.

akshun · May 16, 2014

That does look to be a similar size to the insert i have but i think mine has holes around the inner pipe part. I think mine is more of a spark arrestor but it does quieten it down a lot compared to no insert! Bushfires are a serious risk down here in Oz and i wouldn't ride in summer without one!
Im thinking that with less flow than my 570, your 390 should be fine with the smaller insert regardless?
There are a few threads on here showing how some guys have modified the stock mufflers with reportedly good results, might be worth checking out if your not happy with the new insert.
It seems funny to be talking about making our bikes quieter, am i that old? Ha ha ha!

squi15 · May 16, 2014

Was considering the same exhaust in my 390...any idea of the weight difference between the stock can and the fmf? Do you have the aluminum or titanium 4.1? I think the titanium comes with the insert...

Wallander · May 16, 2014

The 94db insert will be here soon, I will post an image to show the 2 inserts side-by-side.

Yes, quiet is good! And fast. Loud just feels fast.

Weight: I haven't measured it, but "by hand" the difference is small. I have a titanium 4.1, but not the latest one, as you can see on my image, it is a long muffler, the new 4.1 for the 390 is rather short.

akshun · May 16, 2014

When comparing the weight of the whole system it is much lighter! I have the full titanium megabomb system and it is a big improvement over the stock system. Much lighter, not much louder ( with the insert fitted) but a deeper thump sound, noticable increase in mid to top end. I also think the extra flow and the thin wall of the titanium takes the heat away faster too. It is a fairly tight fit through the frame due to the bigger pipe diameter and because it is not oval shaped like the original. I would recommend this system to anybody that doesn't want to spend a million bucks on the akro!

Michigantrailrider · May 18, 2014

Wallander said:
For my FE390 I have the stocker restricted muffler and an FMF 4.1. Bike is EU mapped, ignition set to advanced.

The stock restricted muffler:

I have an insert in the FMF 4.1, but it is rather big in diameter and loud (I'm sure it's not the 94dB version), maybe you can see it in this image:

Comparing these mufflers, it seems the bike is NOT running better with the FMF at low/mid revs, and only slightly better at high revs. I also have an XR400 (now 426cc), and for that bike an open exhaust (FMF Powercore4) made a great difference at low/mid revs, but that is a very different engine, super long stroke compared to the super short stroke FE390.

So the stock muffler seems to work fine, and it is quiet, which is good for me, but it is running hot.

Maybe the FMF 4.1 with a smaller diameter insert would be better, to better suit the FE390 engine?

Many thanks.

I have a 2010 FX 450 and it had a muffler like the one on your 390. The muffler was not US Forrest Service Approved and I needed it to be. I didn't want to spend much so I put a Lexx MXe Slip-On silencer on. I got it from Rocky Mountain for $199.99. They didn't show one for my bike. I bought one for a 2006 KTM 525 EXC because they are pretty much interchangeable as I only had to grind some off of the one strap so it fit into the pocket in the composite rear section.

The exhaust is quiet, US Forrest Service Approved, greatly increases flow, stays much cooler, and made the bike run better.

Just my experience, I hope you get your bike sorted out.

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FE390 stock muffler good enough?

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