o-ring sealed exhaust flanges.
that black oily crap that oozes from the cylinder/pipe junction and drips out the back of the silencer
or spark arrestor. I'm happy to report that my '02 300MXC has an O-ring on the exhaust flange, so
I don't have to go through the annoying rituals described below. These tips apply to the KTM's that
do not have an O-ring exhaust flange, which are many. Without the O-ring, the end of the pipe fits
over the exhaust outlet, metal-on-metal, with nothing keeping the black stuff from leaking out.
Also, the pipe fits around an exhaust flange, which is not as effective as having the pipe fit inside an
exhaust flange (like my Suzuki RMX's did).
Solution #1
Put a layer of red silicone on the outside of the exhaust outlet, put the pipe back on, and let it dry
for a day. I would not recommend putting the silicone on the inside of the pipe. When you push
the pipe over the exhaust outlet, the excess silicone gets forced into the pipe, dries up, breaks off
from exhaust pressure, and then gets stuck in the end of your spark arrestor (if you have a
silencer, this is probably not a problem because it would blow out unobstructed). This method will
work until the pipe gets a couple of rubs against rocks or other hard objects, and then you'll need
to re-seal the junction with more silicone.
Important tip: clean both surfaces until they sparkle, then apply the silicone.
Solution #2
Convert your exhaust flange to the 250SX version that has an O-ring. The part numbers are:
547.05.003.000 (exhaust flange)
0770440030 (Viton O-ring for the flange)
Total cost should be about $20.
CAUTION:
The O-ring flange has a smaller inside diameter than the stock flange. This smaller opening will improve
bottom end somewhat, but will take away some top end power and force you to re-jet.
Spooge out the spark arrestor
No good solution here, but one that helps is replacing the stock spark arrestor with a silencer or an
FMF Turbine Core spark arrestor. I chose the FMF Turbine Core, which is shorter in length than the
stocker, so at least the spooge doesn't drip onto the rear brake.
