January 8, 1992
revised May 9,
Rotax carburetor venting
All Rotax equipped Kitfox's
SkyStar Aircraft, Engineering
purpose of this bulletin is to define the correct configuration of the
carburetor venting system used on Rotax engines.
We have had several reports in the past of builders having
mixture control problems, and our investigations have shown that in
all cases the cause was incorrect carburetor venting.
the 503, 532, and 582 engines, the correct configuration is for each
carburetor to have both venting nipples connected to each other by a
length of Tygon tube. This
tube should have two small holes drilled in it to provide venting.
Do not interconnect the carburetors to each other, and do not
'Y' the tubes to an overboard vent line.
If the lines are 'Y'ed to an overboard line, the different
pressure on the overboard line will result in incorrect carburetor
carburetors will only function normally if the pressure on the vents
is the same as the pressure at the carburetor inlets.
the 912 engine, each carburetor has only a single vent nipple, and the
proper way to vent the carburetor is to connect a short length of
Tygon tube to the nipple and route it to a point just below the
carburetor, tucking the tube under the float bowl attach spring.
Again, it is important to understand that you are trying to
vent the carburetors so that the internal and external pressures at
the carburetor are the same.
vent ports on the carburetors are vents only, and should never have
liquid fuel in them. If you
detect fuel in the vent lines, then you have serious carburetor problems
that should be remedied before further flight.
engines as shipped from Rotax should be equipped with the proper
carburetor vent lines, but you should double check the installation to
insure that your engine will not be forced to run excessively lean.