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YZ125 & 250 FMF Shorty Canister Length?

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Or Pro Circuit. A quick measurement of the canister length would be great, one for each model size as I know they are different. Want to do a little experiment with the stock silencers on both bikes.

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Perhaps of interest, I own a 2010 YZ125 and had a spare stock silencer lying around.

I don't remember the exact length but while at the track I measured an FMF shorty from another rider's YZ125.

Back home I went ahead and cut down my spare silencer to that same length, also installed fresh packing before re-assembly.

 

First thing that stood out when trying it for the 1st time is a noticeably more annoying raspiness / louder dB.

(more what my friends riding around me noticed)

 

Performance wise, big deception...

It ever so slightly increased the 'hit' when getting on the powerband, but in return

had less torque (I know 125's aren't known for torque...) meaning I had to downshift more than usual as it wouldn't

pull a higher gear when re-accelerating out of corners or slower sections like it previously was able to.

To boot, it also had less overrev and fell flat sooner at high rpms than the stock silencer. (running a stock OEM expansion chamber)

 

So much for the experiment...I switched back to the stock length silencer after only one ride.

 

As many here have experienced, if using the stock expansion chamber, the stock length 2006-2010 silencer is hard to beat for overall performance.

 

The current (2011?-2016) YZ125's longer/quieter 'world spec' silencer I've read is somewhat a bit more restrictive

and makes jetting a bit more tricky than the previous silencer/jetting specs so owners of those bikes can benefit to switch to the 2006-2010 silencer.

 

Too bad I messed up a 'good' one (2006-2010) one for such a short and deceiving experiment :

 

01_zpshrrlthrn.jpg

 

02_zpswcfohue2.jpg

Edited by mlatour
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Thanks for your experience and pictures! I was thinking about striking a happy medium between the stock and shorty length, maybe even just cutting up until the 2nd silencer mount.

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Appart from the latest 'longer & quieter' stock YZ silencers which are designed to meet reduced sound levels in many countries / tracks,

 

On the earlier design YZ125 silencers (2006-2010) like mine above, I'm guessing the Yamaha engineers had picked the length that gave the best overall performance.

 

If there was anything to be gained by going a bit shorter, they would have done it already.

 

The 'shorty' design I think came from supercross racing, where having more out-of-the-corner snap was perhaps preferable even if it sacrificed top end overrev.

The shorter body also meant less un-sprung weight on the bike and less prone to crash damage.

Edited by mlatour

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Ken Occoner has video on YouTube about this. He basically shows ya how to cut it and put it back together. I did it on my ported 250 and it did make a noticeable diff in low end torque, as in more torque. I like it for the track because hauling my fat arse out of tight corners is where my times suffer on the track. Over rev is reduced a bit but it didn't bother my style. I would use it for tight woods if I could but no sparky.

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I've got the fmf shorty on my '13 yz 125 and it kinda made it rev quicker . The over rev is gone but I think its cause it revs so qwick now. top end is the same 69 mph on gps with shorty and stock.

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What it sounds like is one thing, how well it performs is another. I prefer the later.

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I have both the FMF shorty and the extra long big OEM silencer on my 2011 yz250, and I prefer the big stock can. If you still need the length I can measure it for you tonight.

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seat of the pants , the bike feels qwicker , pops the front end way easier than before. I only had about 30 minutes with the new fatty to test .the bike is stored 4 winter.

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I have a stock 03 250 with a fmf fatty as the only mod. I ride woods primarily so if I can get some more low end grunt it would be worth it to get my fat ass moving. My dad has the 125 which is an 02 with several mods, if he can get out of the corners without having to downshift as much that would be great. Top end isn't really a concern for ether bike.

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Both bikes would likely see more gain from a rear sprocket change and fine tuning the pilot / needle circuit than any silencer length experiment.

Edited by mlatour
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I'm running 14/51 and do not want to change gearing. Great for me in all situations.

134cc port & polish

'04 PV spring

Fmf fatty

5.75 slide, 20 pilot, stock needle 1st clip, 390 main.

13/50 also have 12/13/14 countershaft and 49 rear sprocket on hand.

I have had a fmf shorty on the 125 at one time and felt that it rolled onto the pipe a little smoother and a little easier.

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I have a stock 03 250 with a fmf fatty as the only mod. I ride woods primarily so if I can get some more low end grunt it would be worth it to get my fat ass moving. My dad has the 125 which is an 02 with several mods, if he can get out of the corners without having to downshift as much that would be great. Top end isn't really a concern for ether bike.

A shorty on a 250 adds snap on the low end and wheel spinning type power bursts. Suggest a FWW, and jetting instead.

Edited by shrubitup

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What is the difference between the 03 and the 04 power valve? Is it the same for 04-current? Because my buddy has a newish one and it pulls like a tractor down low. Never could figure out why the 2 bikes are so different yet have the same engine.

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What is the difference between the 03 and the 04 power valve? Is it the same for 04-current? Because my buddy has a newish one and it pulls like a tractor down low. Never could figure out why the 2 bikes are so different yet have the same engine.

My bad. Thought we were talking KXs. :bonk:

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Always thought I wasn't one to wind out my 125, but rather short shift it more (track has many slow 180° turns, and corner exit traction is often an issue)

until the 'homemade shorty' experience I mentionned above when I realized just how much I actualy did rev it somewhat high and missed the overrev.

Edited by mlatour

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So it seems that nobody likes the shorter silencer, has anyone gone from the 02-10 silencer to the 11+ silencer? Should give more top end?

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Quoted from the Motocross Action 2011 test:

 

Question: IS THE BIKE SLOWER BECAUSE OF THE NEW SILENCER?

 

Answer: Slightly, but not at peak. Yamaha claims that compared to last year’s bike, there is a small dip in midrange power,

but the peak horsepower is the same. This is logical, since longer systems generally don’t hurt top end as much as low end.

 

link to full test: http://motocrossactionmag.com/bike-tests/2011-yamaha-yz125-motocross-test-the-6000-bike-that-the-sport-needs-more-today-than-it-ever-did

 

 

Edited by mlatour

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