DATE:
January 8, 1992 revised
May 9, 1994
SUBJECT:
Rotax carburetor venting
APPLICABILITY:
All Rotax equipped Kitfox's
COMPLIANCE:
Mandatory
FROM:
SkyStar Aircraft, Engineering
Department
The 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.
For 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
performance. The carburetors will
only function normally if the pressure on the vents is the same as the
pressure at the carburetor inlets.
For 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.
The 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.
The 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.