FMF Fatty Pipe
After a short-lived experiment with a heavy, bottom-end-boosting
Gnarly pipe on my 2003 KX250, I wanted to preserve the super-light
feel of the front end. Instead of mounting a heavy Moose steel guard
around the stock pipe, I bought an inventory of cheap stock pipes
from eBay from motocross guys who wanted shiny pipes instead of
black ones. Once or twice a year I'd bang the crap out of a pipe, pull
it off the bike, throw it in the trash and bolt on a $50 replacement.
This continued with the 2004 KX250 for about half the 2006 season.
After moving out of St. Louis, for some reason the dents came more
often and with much greater force in Illinois than Missouri. I was
going through pipes like a Nicole Richie supply of Exlax. A year
earlier I'd found an FMF Fatty pipe on eBay for about $70 delivered
to my door, which by mid-2006 was the last spare pipe in my
inventory. I installed it just before a Wedron, Illinois hare scramble
and used it the rest of the year.
The difference between the Fatty and the stock KX250 pipe was
small but noticeable: a little more throttle response; a bit more "pep"
in the engine. Power-wise, I couldn't tell much difference. My version
of the Fatty was the "Factory" model, which was just like the regular
version except it didn't have a shiny nickel plating. It appears FMF
skipped the nickel plating process to give the pipe a rough
appearance like those found on factory motocross racers. It's
marketing genius: motocross racers hand over an extra $20 or so
and get a pipe that would seem to cost less to manufacture. The
downside is that it always looked rusty. But hey, I'm an off-roader.
The only places my bike shines are where I've applied fresh duct
The Fatty pipe was also a replacement for the stock Akrapovic pipe
on my 2009 KTM 250XC. The stock pipe is fine performance-wise,
but it was made to be very light weight and less than ideal for the
rigors of off-road racing. Even with a carbon fiber pipe guard, the
mounts cracked and the small end of the pipe eventually got pushed
in. The Fatty pipe is a good substitute for strength (although not it in
the same category as the Gnarly); performance is no different than
the stock pipe. If I could do it over again, I'd ditch the stock pipe
before I ever rode the bike, sell it on eBay and recoup some of the
cost of the FMF pipe (which I would be buying at some point anyway).
FMF Gnarly Pipe
In the late 1990's, FMF developed a new pipe specific to off-road
2-stroke motorcycles which promised to deliver more low-end power.
The Gnarly was designed to offer more "grunt" at lower RPM's and
provide resistance to dents, which for you younger folks who've
never owned a 2-stroke dirt bike, is something that happens pretty
often when there's a big fat piece of metal pipe hanging low out the
front side of the engine. I was really not interested in repairing or
replacing pipes on a regular basis, so I ordered up a Gnarly for my
1999 KTM 300EXC when its stock pipe expired. In an effort to avoid
any possibility of dents on my expensive new pipe, I added a Moose
Racing steel pipe guard.
The Gnarly/Moose combo proved to be virtually indestructible. It also
proved to be extremely heavy. I never did a weight comparison, but I
would guess I added a solid 5 pounds or more. This combo worked
so well on the '99 EXC that I did the same for my 2002 KTM 300MXC,
with similar results. I was having such good luck with the Gnarly, I
figured what the heck, I'll put one on my 2003 KX250. That's where
the Gnarly lost its luster. While the pipe did add some low-end power
to the KX, it took away more than I wanted from the top end. The
KTM 300s, in contrast, were so tuned for low-end power (at the
expense of top-end response) that the Gnarly didn't make much
difference in power delivery. The KX250's, on the other hand, were
screamers who demanded to be ridden in the upper-RPM ranges.
Loss of top-end power was more of sacrifice than I was willing to
make. Thus, the Gnarly went to a new eBay home after only a
With the advent of carbon fiber pipe guards, I began using Fatty
pipes when the stock pipes on my various motorcycles wore out. The
carbon fiber guards do a great job in protecting pipes and add very
little weight. The need for pipe strength has lessened, and so did my
love affair with the Gnarly.
FMF Turbine Core
The FMF Turbine Core is a silencer/spark arrestor that is legal for
use in enduros and government-owned riding areas. It's a few
inches shorter than the elongated silencers from the early-2000's
KTM's but slightly longer than the stock silencer on a KX250. Sound
levels are comparable to stock silencers, with the exhaust note on
the KX just a bit softer. Back in the EXC/MXC days of KTM, the stock
silencers were notorious for dripping black oily spooge, and the FMF
Turbine Core helped clean that up somewhat. Some dripping
remained, but the whole exhaust system became more free-flowing.
Instead of spooge dripping onto the brake caliper and pads, it blew
out the back end and sprayed my jersey with tiny black dots. Quality
is typical FMF, which means it's top-notch and installation was
simple. The Turbine Core uses all of the stock mounting, which
means you have to pull off the rubber bushings on the stock unit. I
used a Turbine Core on my first two KTM's in conjunction with
various FMF pipes. For the 2007 Leadbelt Enduro, I installed a
Turbine Core on the 2004 KX250 to meet spark arrestor
requirements. It worked just fine, so I left it on for the rest of the
years I owned that bike.
The only issue I ever had with a Turbine Core was at the July 2001
Tebbetts, Missouri hare scramble. On that day I was riding my 1999
KTM 300EXC and the stinger tube broke off from the silencer body.
I called the FMF warranty department and they agreed to replace it
free of charge, even though it was about 8 months past its warranty.
Apparently the KTM's had enough flex in the pipe/silencer joint that
several FMF silencers had broken on the KTM's. Probably didn't
help that my sub-frame had a slight tweak (thanks to Belleville in '99)
that caused the mounts to be off slightly, requiring a bit of
persuasion to get the silencer mounted. Over time, that was
probably what caused the weakness that broke the thing. The new
Turbine Core appeared to have a thicker weld where the stinger
tube met the silencer body.
I bought a slightly used Turbine Core for my 2003 KX250 and never
used it until the AMA's National Enduro Series went to a
closed-course, rally-style format in 2007 that required no
timekeeping. Without the need for an odometer, I brought the 2004
KX250 to the Leadbelt Enduro and bolted on the Turbine Core. It
passed the sound test and didn't affect power delivery at any
One of the downsides to the Turbine Core is that if you want to fully
disassemble it down to the end cap, rivets must be drilled out and
replaced with some other type of fastener (unless you have the tools
to re-rivet the end cap). About the only thing I've found that works
halfway decent is very large-diameter sheet metal screws. The
challenge is finding a "fat" enough screw to match the diameter of
the internal clips that hold the insides of the end cap against the
outer shell. The next challenge is keeping the screws from falling
out. The best I could do is #14 sheet metal screws, 3/4" long. This
does require drilling to make the original rivet holes a little larger.
The only way I've found to effectively keep the screws in place is
dipping them in JB Weld and screwing them in (they'll still come out
the next time you need to disassemble the end cap).
Moose Racing Steel Pipe Guard
One word: STRONG! Six more words: Pain in the ass to install! But
well worth the effort because it's never suffered any damage
whatsoever. Thick construction makes it difficult to shape around
the pipe, but a large rubber mallet and a lot of pounding will
eventually get it mounted properly (a vice helps; also, I used a floor
jack stand to aid in the pounding/shaping). The guard is relatively
light, not too expensive and will probably never break. Good stuff.
E-Line Carbon Fiber Pipe Guard
When I bolted on a new FMF Fatty pipe for my '04 KX250, I decided
it was time to step up and give it some real protection. To preserve
the light feel of the KX's front end, I wanted to go light, so I shelled
out some serious dough and picked up an E-Line pipe guard. These
are not cheap - about $140 - but they are simple to install and very
lightweight. The only downside besides price is they do scuff easily.
However, for me, the word "scuff" is completely neutral as it applies
to my dirt bikes. This is the guard to have. I'm now using one on my
Click on pictures to
see larger image
|After 2 years, the KX250
pipe guard was pretty
well done. The hole is
where the front wheel
kicked up trail junk.
But it did a fine job of
protecting the pipe.