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

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 tape.

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 couple rides.

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

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
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 noticeable level.

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.
Click on pictures to
see larger image
After 2 years, the
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
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