MA Series Carburetors are reliable and easy to maintain. However, most will require service before your engine hits its' TBO. Typically the first indication of trouble will be evident at idle. An abnormally lean idle will typically hint towards a worn throttleshaft and a rich idle will indicate a worn needle/seat or float. Although the MA carburetors appear simple we recommend that one take care when attempting a repair or modification on your own. Below are a few of the common "mistakes" we find.
MA Series Carburetors
RSA Fuel Servos
The RSA Fuel Servo is a work of art. With proper care, these Servos will easily provide many years of reliable service. The most common repair is fixing a leaking mixture assembly. Other than flat packing's the most common indication that your RSA is nearing OH is a rich condition throughout the whole rpm range. This rich condition is a result of diaphragm; stretch, contamination or leakage. While a cleaning and adjustment might be able to repair this rich condition; typically it can only be eliminated by an overhaul.
This is a picture of the airside of an RSA diaphragm. If observed closely, one can note the oil residue. This common buildup of oil can result in bad fuel flow. Sometimes the diaphragms can be unstacked, cleaned and reinstalled without the need for an overhaul. However, if the diaphragm is too worn, a overhaul maybe required.
This leaking mixture shaft is a result of the improper stacking of the spring, cup and retainer.
The use of a punch to "repair" a worn mixture shaft bushing is not an authorized repair practice. Sometimes this type of damage is not easily reversible.
Make sure the new gaskets have all of the bits removed, otherwise you will restrict your air circuits.
MA Series Floats
In 2009 SB-2 was released which called for the replacement of all brass, foam and hallow plastic floats. Although many carbs are still sold with brass floats we recommend the installation of the new blue epoxy floats. Here are a few reasons why;
The plastic hallow floats fill with fuel and sink. If you have this float in your carb please have it removed. A sunk float mid-flight will ruin your day.
Brass floats are soldered together and sometimes that solder fails. Here is a brass float that lost a pontoon. The pilot reported inconsistent fuel flow.
Brass floats swing on a steel pin. Overtime the brass will wear on the steel and the float will become loose. The float will eventually contact with the bowl and could get hung-up. Again, ruining your day.