Don’t mistake cam chain clatter for a
blown top-end on a KTM.
THE DEATH RATTLE
I bought a used 2011 KTM
250SXF. When I start the bike, it
makes a terrible clatter. I’m afraid
that the valves are out of adjust-
ment. Once the bike warms up, the
noise disappears. What’s happening?
Your 250SXF has a hydraulic
cam-chain tensioner instead of a
spring-loaded one. It takes a few
seconds to build pressure in the
system. Once the hydraulic pressure
catches up, the slapping cam-chain
noise goes away. No problem. ;
Bikes pop when the exhaust pipe leaks.
WHAT CAUSES BACKFIRING?
My bike runs great, but when I
shut the throttle off it backfires like
crazy. What causes this?
There are two possible causes: (1)
An air leak at the head pipe allows
cold air to be sucked in and ignite.
If you have an aftermarket pipe,
it could be leaking at the slip-on
fitting between the head pipe and
mid-pipe. If you didn’t replace the
exhaust pipe gasket the last time
you removed your pipe, this could be
the cause. ( 2) For some reason that
we don’t fully understand, burned-out muffler packing will make a bike
pop on deceleration.