1. Why do I need a breather?
Air in the container expands and contracts with
temperature changes - which can be significant if the container is mounted in
the typical underseat area.
If the air in the container can't expand and contract
freely then this may cause sealing problems in the container's cap and leads. The same point applies to trapping/kinking the breather.
If the pump is forced to suck too hard, it may cause
seals in the lines to pop, allowing the pump to draw air, instead of oil from
the container - and will of course make the oil delivery unprdictable.
2. Is the breather tube routing important?
The breather tube's
outlet should be well above the highest point of the breather intake in the
If the tube fills with
oil, and the outlet is below the intake, there will be a syphon
action which can cause oil to drain out. This is potentially dangerous
and can cause an accident if it gets on the back tyre
Re-position the container so that the breather intake
does not come under the oil level
Do not overfill the container (as a rule of thumb, the
oil level should be at least 10mm below the breather inlet)
Do not locate the container with the cap facing the left
of the bike. When the bike is on its side-stand, the breather could become
submerged and allow the oil to drain out.
Check the breather tube is not trapped or kinked
3. What is the best breather tube routing? Any other tips?
The breather is best routed along the length axis of the
bike, with its outlet at least 5cm above the highest point you
can foresee the for breather intake (eg. when the bike is on its
The greater the height difference between the intake and
outlet, the better
The longer the breather tube, in general the better
(30cm is a good length, but there's no harm in a longer tube if you have the
space - you can even coil it up)
4. What should I do if I see the breather tube is filled with oil?
Try and work out why the breather intake came to be
submerged in the first place
Don't forget that the higher the oil level, the more
often the breather intake will be submerged temporarily under braking,
acceleration and cornering forces. This is no problem as long as the breather
intake is normally exposed, that's to say, located in the air in the top of the
Bear in mind, if the tube has oil in it, and the air in
the container heats up and expands, then this oil can be blown out
because it forms a plug.
If you clear the oil (see below), and then soon after
see that the line is again filled, then
Consider running with a lower oil level in
and/or ensure you use a long breather line with a high
outlet (the shorter the line the more likely that oil can start a syphon
To clear an oil-filled breather line:
Ensure the breather intake is not currently submerged
Unplug the breather line from the brass tubing and drain
it (blow into it if necessary)
Reconnect the line