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YZ250 FMF Gnarly Woods pipe test report

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OK, first my bike setup.

 

2013 Yamaha YZ250

 

G2 Throttle Tamer

 

11oz flywheel weight

 

Stock pipe and silencer

 

13x50 gearing

 

Stock timing

 

I first installed an FMF Turbine Core 2 silencer with the stock pipe. No change in sound or power.

 

Then I installed the Gnarly Woods pipe with the TC2 and went for a ride. For the first part of the ride I was riding in tight single track and could not tell much of a difference. Then I hit some technical hill climbs and it's there the pipe made a big difference. The power comes on sooner and the hit is spread out over more RPM's. The pipe did not seem to effect the top end.

 

I was torquing up hills where before I had to be on the pipe to make. The bike now has much better grunt than before.

 

Night and day difference? No. Worth the money for super tight knarly terrain? Yep! More open terrain? Maybe not.

 

I like to climb technical hills so for what I like to do this pipe makes my life easier. I can now short shift into second at the base and the bike just keeps pulling without falling off the pipe.

 

 

 

 

 

 

 

 

 

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Were you able to leave the jetting stock or did you have to change anything?

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The jetting is still stock. I took a plug reading before I installed the pipe and it was a perfect light brown. I am curious to get another plug reading with the new pipe. FMF included a jetting chart and it showed stock jet sizes. The elevation I ride at is 380' above sea level.

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FMF included a jetting chart and it showed stock jet sizes.

Cool - thanks.

 

 I gor here ans I'm searching for jetting info as my Gnarly arrives tomorrow.

 

BTW I have the same bike as you, ride about the same areas, but my mods are a bit different.

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Top end killer:  what I'm gonna try with the Gnarly is putting the 50t back on the rear.

 

My priority is getting some lower end grunt - which is where I mostly ride.

 

I don't ride WFO all that much - tight trails with short short blasts on open areas.

 

We'll just have to see how it goes.

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Top end killer: what I'm gonna try with the Gnarly is putting the 50t back on the rear.

My priority is getting some lower end grunt - which is where I mostly ride.

I don't ride WFO all that much - tight trails with short short blasts on open areas.

We'll just have to see how it goes.

Which is fine if you never like to open it up.....

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Shit is it that bad?

 

I would say the power dies off around 2000rpms earlier than with the stock pipe.  It's a good pipe for tight woods riding, but that's about it.  I loved it for that purpose, but I did miss the top end on the more open trails.

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Which is fine if you never like to open it up.....

The areas where I DO open it up are mostly the fire roads connecting the "fun areas".  I just got my hands on a Gnarly for little investment and I have 1 huge dent to remove and it's going on.  If I decide that it's just TOO MUCH of a loss of top end, I'll sell it and go with a Fatty.

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I would say the power dies off around 2000rpms earlier than with the stock pipe.  It's a good pipe for tight woods riding, but that's about it.  I loved it for that purpose, but I did miss the top end on the more open trails.

Thanks.

 

Guess time will tell.  Pipe will be here today and I'll ride it Sunday.

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Thanks.

 

Guess time will tell.  Pipe will be here today and I'll ride it Sunday.

Come back here and tell us what you think.

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Come back here and tell us what you think.

OK.

 

I had cortisone inj in my hip yesterday, so may not go WFO for 2 weeks or so.

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2000 rpm is a huge exaggeration, or something in the powervalve is broken on RiderX's bike. 

 

Realistically the power valve opens around 6000 rpm on these bikes, power peaks around 8300-8500 rpm, and by 9000 rpm power is falling like a rock. 

 

 

When I went from a FMF Fatty to a Gnarly on my bike I would guess that power came on 300-500 rpm sooner, peak was likely 300-ish rpm sooner, and the reason topend felt like it was murdered was because the bike lost any and all over rev. My hourmeter/tach would showed I could pull 9400 rpm in 4th, but this was WAY past peak power. Bike liked to be shifted in the mid 8000's. 

 

 

What bugged me most on the Gnarly was the flat spot it created in the midrange. Seemed to want some power valve tuning. It was as if the pipe needed the power valve to open sooner, no amount of jetting could help it. The Fatty was very linear, the Gnarly made great low end, plateaued for a moment, then had a big hit and decent top end power. Even racing harescrambles in the desert of AZ I never felt the need for more peak power.

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Interesting observations.  I'm going from a PC Platinum so if my rough looking Gnarly is just too tame or quirky, I'll order a Fatty for sure.

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