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 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 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 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
I don't even know if these things are sold anymore, but the time I
bought one for a two-stroke bike many years ago, I can describe in
o
ne word: STRONG!  For another six  words, I can safely say: Pain in
the ass to install!
This was the kind of pipe guard that has to be bent
and shaped around the contours of the fat part of a two-stroke
exhaust pipe.
But the effort was worth it because the guard protected
the pipe like a champ
.  Thick construction made it difficult to shape
around the pipe, but a large rubber mallet and a lot of pounding
w
ould eventually get it mounted properly (a vice helps; also, I used a
floor jack stand to aid in the pounding/shaping).  The guard
was
actually
relatively light, not too expensive and never even thought
about breaking
. It was good stuff in the late-1990s, but with the
advent of extreme enduro, there are all kinds of other manufacturers
selling crazy good pipe protection.


Carbon Fiber Pipe Guards
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
in the mid-2000s - 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.


Since then, I've used several different carbon fiber pipe guards from a
couple of aftermarket companies. These are the guards to have, if you
want to keep the bike light.
Exhaust
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