[The following information is general in nature and not intended to circumvent the actual manufacturer's official documents and requirements.]
Rotax has just released a mandatory SB which may affect your carbureted Rotax engine. Owner/operators should pay special attention to the requirements of this information release and in particular the details and requirements as outlined in the actual SB.
Compliance to this SB is a mandatory requirement and affects serial specific engines and carbs as well as any engines or carbs which may have been serviced with new floats (part number 861 184) from spare parts which were produced from approximately June 1st 2012 onward (check SB for details).
The issue stems from a possible manufacturing deviance leading to some floats absorbing fuel, which increases their weight affecting the float level in the carb. Possible effects may be a rough running engine especially at low speeds, engine stoppage and/or fuel leakage in the area of the carburetor venting.
Rotax has developed a quick test method using a special assembly of parts (syringe which measures in ml with rubber line and diffuser tube adaptor) resulting in a effective “test tool” for checking if your floats are working properly or not (see SB for the specific list of parts required to make up the test tool). The process allows in most cases for checking the float level while the carbs remain installed on the aircraft.
For this test you must run the engine for two minutes to assure the float chambers are full, then after shutdown remove the carb vent line, then the choke plate cover (four screws), and using a special Rotax supplied test tool (basically a syringe which measures ml with a short rubber line and size specific tube adaptor end), inject a measured amount of fuel into the carb float chamber until it just starts coming out of the carb overflow (see SB for the details). At this point you measure exactly how much fuel you injected into the chamber by which you can determine if it falls into the correct range or not (between 23ml to 40ml).
If it fails then you must remove both floats and weigh them together on a precision gram scale (+- tolerance of 0.1 grams), and if the two floats together weigh over 7 grams then they both need to be replaced. (Floats are supplied in pairs.)
Until Rotax comes up with a new float design, all floats which have come from replacement parts since June 1st 2012, or which are already installed in carb serial numbers and/or engine serial numbers affected by this SB must be checked every 25 hours of run time or every 60 days - whichever comes first.
At time of this release the required test tool (special syringe with rubber line and diffuser tube adaptor) may not in all cases be immediately available from your Rotax Service Provider, but we are assured that rush orders for same are in place.
An important point to keep in mind regarding this SB is that even if you replace your floats with new of same part number 861 184, the mandatory 25 hour/60 day checks are still required until such time as Rotax can supply a completely new design of float, (which they are working on) - more information on same will follow as it becomes available. Also, each time the test is performed, a new choke cover gasket Rotax part# 950 030 must be installed.
In the meantime, for any engines which are suspected of having carb float issues, or are running up to the mandatory 25 hour/60 day check (whichever comes first) - but for which the Owner/Operator cannot wait for the special “Test Syringe Tool” from their service provider - the SB also outlines a method for weighing the floats on an accurate gram scale to determine if they are good or not. This alternate test requires that the carb floats be removed from the carbs.
View the Rotax-Owner video release on this bulletin.
